pinctrl: pinctrl-single: add header include guard

Add a header include guard just in case.

Signed-off-by: Masahiro Yamada <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

include/linux/platform_data/pinctrl-single.h

···
 /* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _PINCTRL_SINGLE_H
+#define _PINCTRL_SINGLE_H
+
 /**
  * irq:		optional wake-up interrupt
  * rearm:	optional soc specific rearm function
···
 	int irq;
 	void (*rearm)(void);
 };
+
+#endif /* _PINCTRL_SINGLE_H */