Clear LED matrix without startup test

Marlin/src/feature/Max7219_Debug_LEDs.cpp

   #endif
 }
 
+void Max7219_Clear() {
+  for (uint8_t r = 0; r < 8; r++) _Max7219_Set_Reg(r, 0);
+}
+
 void Max7219_Set_2_Rows(const uint8_t y, uint16_t val) {
   if (y > 6) return Max7219_Error(PSTR("Max7219_Set_2_Rows"), y, val);
   Max7219_Set_Row(y + 0, val & 0xFF); val >>= 8;

Marlin/src/feature/Max7219_Debug_LEDs.h

 void Max7219_Set_Row(const uint8_t row, const uint8_t val);
 void Max7219_Clear_Row(const uint8_t row);
 
+// Quickly clear the whole matrix
+void Max7219_Clear();
+
 // Apply custom code to update the matrix
 void Max7219_idle_tasks();
 

Marlin/src/gcode/feature/leds/M7219.cpp

  */
 void GcodeSuite::M7219() {
   if (parser.seen('I'))
-    Max7219_init();
+    Max7219_Clear();
   else if (parser.seenval('R')) {
     const uint8_t r = parser.value_int();
     Max7219_Set_Row(r, parser.byteval('V'));