drm/i915: fix sparse warnings: make symbols static

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@linux.ie>
diff --git a/drivers/gpu/drm/i915/i915_opregion.c b/drivers/gpu/drm/i915/i915_opregion.c
index 13ae731..ff01283 100644
--- a/drivers/gpu/drm/i915/i915_opregion.c
+++ b/drivers/gpu/drm/i915/i915_opregion.c
@@ -257,8 +257,8 @@
 
 static struct intel_opregion *system_opregion;
 
-int intel_opregion_video_event(struct notifier_block *nb, unsigned long val,
-			       void *data)
+static int intel_opregion_video_event(struct notifier_block *nb,
+				      unsigned long val, void *data)
 {
 	/* The only video events relevant to opregion are 0x80. These indicate
 	   either a docking event, lid switch or display switch request. In