drm/vc4: drv: Add include guards

vc4_drv.h doesn't have any include guards which prevents it from being
included twice. Let's add them.
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/68e89e315c4c35b313efc277c9642eca684e0ade.1590594512.git-series.maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_drv.h

@@ -2,6 +2,8 @@
 /*
  * Copyright (C) 2015 Broadcom
  */
+#ifndef _VC4_DRV_H_
+#define _VC4_DRV_H_
 
 #include <linux/delay.h>
 #include <linux/refcount.h>
@@ -897,3 +899,5 @@ int vc4_perfmon_destroy_ioctl(struct drm_device *dev, void *data,
 			      struct drm_file *file_priv);
 int vc4_perfmon_get_values_ioctl(struct drm_device *dev, void *data,
 				 struct drm_file *file_priv);
+
+#endif /* _VC4_DRV_H_ */