Add include guards to some headers

Marlin/src/feature/Max7219_Debug_LEDs.h

@@ -19,6 +19,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * This module is off by default, but can be enabled to facilitate the display of

Marlin/src/feature/prusa_MMU2/mmu2.h

@@ -19,7 +19,6 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
-
 #pragma once
 
 #include "../../inc/MarlinConfig.h"