Fix M503 output for M907 motor current (#19777)

Co-authored-by: Scott Lahteine <github@thinkyhead.com>

Marlin/src/module/settings.cpp

       CONFIG_ECHO_HEADING("Stepper motor currents:");
       CONFIG_ECHO_START();
       #if HAS_MOTOR_CURRENT_PWM
-        SERIAL_ECHOLNPAIR_P(
-            PSTR("  M907 X"), stepper.motor_current_setting[0]
-          , SP_Z_STR, stepper.motor_current_setting[1]
-          , SP_E_STR, stepper.motor_current_setting[2]
+        SERIAL_ECHOLNPAIR_P(                                   // PWM-based has 3 values:
+            PSTR("  M907 X"), stepper.motor_current_setting[0] // X and Y
+                  , SP_Z_STR, stepper.motor_current_setting[1] // Z
+                  , SP_E_STR, stepper.motor_current_setting[2] // E
         );
       #elif HAS_MOTOR_CURRENT_SPI
-        SERIAL_ECHOPGM("  M907");
-        LOOP_L_N(q, MOTOR_CURRENT_COUNT) {
-          SERIAL_CHAR(' ');
-          SERIAL_CHAR(axis_codes[q]);
+        SERIAL_ECHOPGM("  M907");                              // SPI-based has 5 values:
+        LOOP_XYZE(q) {                                         // X Y Z E (map to X Y Z E0 by default)
+          SERIAL_CHAR(' ', axis_codes[q]);
           SERIAL_ECHO(stepper.motor_current_setting[q]);
         }
-      #endif
+        SERIAL_CHAR(' ', 'B');                                 // B (maps to E1 by default)
+        SERIAL_ECHOLN(stepper.motor_current_setting[4]);
+      #endif
+    #elif HAS_MOTOR_CURRENT_I2C                                // i2c-based has any number of values
+      // Values sent over i2c are not stored.
+      // Indexes map directly to drivers, not axes.
+    #elif HAS_MOTOR_CURRENT_DAC                                // DAC-based has 4 values, for X Y Z E
+      // Values sent over i2c are not stored. Uses indirect mapping.
     #endif
 
     /**

Marlin/src/module/stepper.cpp

   #if HAS_MOTOR_CURRENT_SPI || HAS_MOTOR_CURRENT_PWM
 
     void Stepper::set_digipot_current(const uint8_t driver, const int16_t current) {
-      if (WITHIN(driver, 0, COUNT(motor_current_setting) - 1))
+      if (WITHIN(driver, 0, MOTOR_CURRENT_COUNT - 1))
         motor_current_setting[driver] = current; // update motor_current_setting
 
       if (!initialized) return;

Marlin/src/pins/rambo/pins_RAMBO.h

 #define E1_MS2_PIN                            64
 
 #define DIGIPOTSS_PIN                         38
-#define DIGIPOT_CHANNELS  { 4,5,3,0,1 }           // X Y Z E0 E1 digipot channels to stepper driver mapping
+#define DIGIPOT_CHANNELS { 4, 5, 3, 0, 1 }        // X Y Z E0 E1 digipot channels to stepper driver mapping
 #ifndef DIGIPOT_MOTOR_CURRENT
   #define DIGIPOT_MOTOR_CURRENT { 135,135,135,135,135 }   // Values 0-255 (RAMBO 135 = ~0.75A, 185 = ~1A)
 #endif

Marlin/src/pins/rambo/pins_SCOOVO_X9H.h

 #define E1_MS2_PIN                            64
 
 #define DIGIPOTSS_PIN                         38
-#define DIGIPOT_CHANNELS {4,5,3,0,1}              // X Y Z E0 E1 digipot channels to stepper driver mapping
+#define DIGIPOT_CHANNELS { 4, 5, 3, 0, 1 }        // X Y Z E0 E1 digipot channels to stepper driver mapping
 
 //
 // Temperature Sensors

Marlin/src/pins/ramps/pins_BQ_ZUM_MEGA_3D.h

 // Steppers
 //
 #define DIGIPOTSS_PIN                         22
-#define DIGIPOT_CHANNELS   { 4, 5, 3, 0, 1 }
+#define DIGIPOT_CHANNELS { 4, 5, 3, 0, 1 }
 
 //
 // Temperature Sensors