Fix M503 output for M907 motor current (#19777)

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

Marlin/src/module/settings.cpp

@@ -3719,19 +3719,25 @@ void MarlinSettings::reset() {
       CONFIG_ECHO_HEADING("Stepper motor currents:");
       CONFIG_ECHO_START();
       #if HAS_MOTOR_CURRENT_PWM
-        SERIAL_ECHOLNPAIR_P(
+        SERIAL_ECHOLNPAIR_P(                                   // PWM-based has 3 values:
-            PSTR("  M907 X"), stepper.motor_current_setting[0]
+            PSTR("  M907 X"), stepper.motor_current_setting[0] // X and Y
-          , SP_Z_STR, stepper.motor_current_setting[1]
+                  , SP_Z_STR, stepper.motor_current_setting[1] // Z
-          , SP_E_STR, stepper.motor_current_setting[2]
+                  , SP_E_STR, stepper.motor_current_setting[2] // E
         );
       #elif HAS_MOTOR_CURRENT_SPI
-        SERIAL_ECHOPGM("  M907");
+        SERIAL_ECHOPGM("  M907");                              // SPI-based has 5 values:
-        LOOP_L_N(q, MOTOR_CURRENT_COUNT) {
+        LOOP_XYZE(q) {                                         // X Y Z E (map to X Y Z E0 by default)
-          SERIAL_CHAR(' ');
+          SERIAL_CHAR(' ', axis_codes[q]);
-          SERIAL_CHAR(axis_codes[q]);
           SERIAL_ECHO(stepper.motor_current_setting[q]);
         }
+        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

@@ -2962,7 +2962,7 @@ void Stepper::report_positions() {
   #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;