[media] v4l: async: check for v4l2_dev in v4l2_async_notifier_register()

Add a check for v4l2_dev to v4l2_async_notifier_register() as to fail as
early as possible since this will fail later in v4l2_async_test_notify().
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

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

@@ -148,7 +148,8 @@ int v4l2_async_notifier_register(struct v4l2_device *v4l2_dev,
 	struct v4l2_async_subdev *asd;
 	int i;
 
-	if (!notifier->num_subdevs || notifier->num_subdevs > V4L2_MAX_SUBDEVS)
+	if (!v4l2_dev || !notifier->num_subdevs ||
+	    notifier->num_subdevs > V4L2_MAX_SUBDEVS)
 		return -EINVAL;
 
 	notifier->v4l2_dev = v4l2_dev;