[media] V4L: Add v4l2_event_subdev_unsubscribe() helper function

Add a v4l2 core helper function that can be used as the subdev
.unsubscribe_event handler. This allows to eliminate some
boilerplate from drivers that are only handling the control events.

Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/v4l2-core/v4l2-event.c

@@ -311,3 +311,10 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
 	return 0;
 }
 EXPORT_SYMBOL_GPL(v4l2_event_unsubscribe);
+
+int v4l2_event_subdev_unsubscribe(struct v4l2_subdev *sd, struct v4l2_fh *fh,
+				  struct v4l2_event_subscription *sub)
+{
+	return v4l2_event_unsubscribe(fh, sub);
+}
+EXPORT_SYMBOL_GPL(v4l2_event_subdev_unsubscribe);