Fix some AVR HAL code style

Marlin/src/HAL/HAL_AVR/fastio_AVR.h

@@ -26,8 +26,8 @@
  * Contributed by Triffid_Hunter. Modified by Kliment and the Marlin team.
  */
 
-#ifndef _FASTIO_ARDUINO_H
-#define _FASTIO_ARDUINO_H
+#ifndef _FASTIO_ARDUINO_H_
+#define _FASTIO_ARDUINO_H_
 
 #include <avr/io.h>
 #include "../../core/macros.h"
@@ -323,4 +323,4 @@ typedef enum {
 // finally - the macro that tells us if a pin is an available hardware PWM
 #define USEABLE_HARDWARE_PWM(p) (PWM_PINS(p) && !PWM_CHK(p))
 
-#endif // _FASTIO_ARDUINO_H
+#endif // _FASTIO_ARDUINO_H_