ARM: at91: generic.h: Add include safe guards

The generic.h header file doesn't have any safe guards against multiple
inclusion. It only worked so far because all the symbols defined in it were
extern, but this is a rather fragile assumption.
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: NBoris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NNicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/generic.h

@@ -8,6 +8,9 @@
  * published by the Free Software Foundation.
  */
 
+#ifndef _AT91_GENERIC_H
+#define _AT91_GENERIC_H
+
 #include <linux/clkdev.h>
 #include <linux/of.h>
 #include <linux/reboot.h>
@@ -84,3 +87,5 @@ extern int  __init at91_gpio_of_irq_setup(struct device_node *node,
 					  struct device_node *parent);
 
 extern u32 at91_get_extern_irq(void);
+
+#endif /* _AT91_GENERIC_H */