[media] v4l2-async: Don't fail if registered_async isn't implemented

After sub-dev registration in v4l2_async_test_notify(), the v4l2-async
core calls the registered_async callback but if a sub-dev driver does
not implement it, v4l2_subdev_call() will return a -ENOIOCTLCMD which
should not be considered an error.
Reported-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Tested-by: Benoit Parrot <bparrot@ti.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

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

@@ -120,7 +120,7 @@ static int v4l2_async_test_notify(struct v4l2_async_notifier *notifier,
 	}
 
 	ret = v4l2_subdev_call(sd, core, registered_async);
-	if (ret < 0) {
+	if (ret < 0 && ret != -ENOIOCTLCMD) {
 		if (notifier->unbind)
 			notifier->unbind(notifier, sd, asd);
 		return ret;