Remove 'const' from PersistentStore::capacity

Marlin/src/HAL/HAL_AVR/persistent_store_eeprom.cpp

   return false;  // always assume success for AVR's
 }
 
-const size_t PersistentStore::capacity() { return E2END + 1; }
+size_t PersistentStore::capacity() { return E2END + 1; }
 
 #endif // EEPROM_SETTINGS
 #endif // __AVR__

Marlin/src/HAL/HAL_DUE/persistent_store_eeprom.cpp

   return false;
 }
 
-const size_t PersistentStore::capacity() { return E2END + 1; }
+size_t PersistentStore::capacity() { return E2END + 1; }
 
 #endif // EEPROM_SETTINGS
 #endif // ARDUINO_ARCH_SAM

Marlin/src/HAL/HAL_LPC1768/HAL.cpp

 
 // possible config options if something similar is extended to more platforms.
 #define ADC_USE_MEDIAN_FILTER          // Filter out erroneous readings
-#define ADC_MEDIAN_FILTER_SIZE    (23) // Higher values increase step delay (phase shift),
+#define ADC_MEDIAN_FILTER_SIZE     23  // Higher values increase step delay (phase shift),
                                        // (ADC_MEDIAN_FILTER_SIZE + 1) / 2 sample step delay (12 samples @ 500Hz: 24ms phase shift)
                                        // Memory usage per ADC channel (bytes): (6 * ADC_MEDIAN_FILTER_SIZE) + 16
                                        // 8 * ((6 * 23) + 16 ) = 1232 Bytes for 8 channels
 
 #define ADC_USE_LOWPASS_FILTER         // Filter out high frequency noise
-#define ADC_LOWPASS_K_VALUE       (6)  // Higher values increase rise time
+#define ADC_LOWPASS_K_VALUE         6  // Higher values increase rise time
                                        // Rise time sample delays for 100% signal convergence on full range step
                                        // (1 : 13, 2 : 32, 3 : 67, 4 : 139, 5 : 281, 6 : 565, 7 : 1135, 8 : 2273)
                                        // K = 6, 565 samples, 500Hz sample rate, 1.13s convergence on full range step
       datum = STOPPER + 1;                  // No stoppers allowed.
     }
 
-    if ( (++datpoint - buffer) >= ADC_MEDIAN_FILTER_SIZE) {
+    if ( (++datpoint - buffer) >= (ADC_MEDIAN_FILTER_SIZE)) {
       datpoint = buffer;                    // Increment and wrap data in pointer.
     }
 
 
 struct LowpassFilter {
   uint32_t data_delay = 0;
-  uint16_t update(uint16_t value) {
-    data_delay = data_delay - (data_delay >> ADC_LOWPASS_K_VALUE) + value;
-    return (uint16_t)(data_delay >> ADC_LOWPASS_K_VALUE);
+  uint16_t update(const uint16_t value) {
+    data_delay -= (data_delay >> (ADC_LOWPASS_K_VALUE)) - value;
+    return (uint16_t)(data_delay >> (ADC_LOWPASS_K_VALUE));
   }
 };
 

Marlin/src/HAL/HAL_LPC1768/persistent_store_sdcard.cpp

   return bytes_read != size;  // return true for any error
 }
 
-const size_t PersistentStore::capacity() { return 4096; } // 4KiB of Emulated EEPROM
+size_t PersistentStore::capacity() { return 4096; } // 4KiB of Emulated EEPROM
 
 #endif // !FLASH_EEPROM
 #endif // EEPROM_SETTINGS

Marlin/src/HAL/HAL_STM32F1/persistent_store_flash.cpp

   return false;
 }
 
-const size_t PersistentStore::capacity() { return E2END + 1; }
+size_t PersistentStore::capacity() { return E2END + 1; }
 
 #endif // EEPROM_SETTINGS && EEPROM FLASH
 #endif // __STM32F1__

Marlin/src/HAL/HAL_STM32F1/persistent_store_sdcard.cpp

   return false;
 }
 
-const size_t PersistentStore::capacity() { return HAL_STM32F1_EEPROM_SIZE; }
+size_t PersistentStore::capacity() { return HAL_STM32F1_EEPROM_SIZE; }
 
 #endif // EEPROM_SETTINGS
 

Marlin/src/HAL/HAL_STM32F4/persistent_store_eeprom.cpp

   return false;
 }
 
-const size_t PersistentStore::capacity() { return E2END + 1; }
+size_t PersistentStore::capacity() { return E2END + 1; }
 
 #endif // EEPROM_SETTINGS
 #endif // STM32F4 || STM32F4xx

Marlin/src/HAL/HAL_STM32F7/persistent_store_eeprom.cpp

   return false;
 }
 
-const size_t PersistentStore::capacity() { return E2END + 1; }
+size_t PersistentStore::capacity() { return E2END + 1; }
 
 #endif // EEPROM_SETTINGS
 #endif // STM32F7

Marlin/src/HAL/HAL_TEENSY35_36/persistent_store_eeprom.cpp

   return false;
 }
 
-const size_t PersistentStore::capacity() { return E2END + 1; }
+size_t PersistentStore::capacity() { return E2END + 1; }
 
 #endif // EEPROM_SETTINGS
 #endif // __MK64FX512__ || __MK66FX1M0__

Marlin/src/HAL/shared/persistent_store_api.h

   static bool access_finish();
   static bool write_data(int &pos, const uint8_t *value, size_t size, uint16_t *crc);
   static bool read_data(int &pos, uint8_t* value, size_t size, uint16_t *crc, const bool writing=true);
-  static const size_t capacity();
+  static size_t capacity();
 
   static inline bool write_data(const int pos, uint8_t* value, const size_t size) {
     int data_pos = pos;