cores: arduino: overloads.h: add pragma once

Add `#pragma once` to guard duplicated including.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

Author: soburi

cores/arduino/overloads.h

@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#pragma once
+
 #ifdef CONFIG_DAC
 
 void analogWrite(enum dacPins pinNumber, int value);