🐛 Fix some BTT SKR2 pins (#22558)

Marlin/src/pins/stm32f4/pins_BTT_SKR_V2_0_common.h

 #endif
 
 //
-// NeoPixel LED
-//
-#ifndef NEOPIXEL_PIN
-  #define NEOPIXEL_PIN                      PE6
-#endif
-
-//
 // Control pin of driver/heater/fan power supply
 //
 #define SAFE_POWER_PIN                      PC13
 #endif
 
 //
+// NeoPixel LED
+//
+#ifndef NEOPIXEL_PIN
+  #define NEOPIXEL_PIN                      PE6
+#endif
+
+//
 // WIFI
 //
 

ini/stm32f4.ini

                               -DUSE_USBHOST_HS -DUSE_USB_HS_IN_FS
                               -DUSBD_IRQ_PRIO=5 -DUSBD_IRQ_SUBPRIO=6
                               -DHSE_VALUE=8000000U -DHAL_SD_MODULE_ENABLED
+                              -DPIN_SERIAL3_RX=PD_9 -DPIN_SERIAL3_TX=PD_8
 
 #
 # BigTreeTech SKR V2.0 (STM32F407VGT6 ARM Cortex-M4) with USB Media Share Support