[media] v4l2-event: Add v4l2_subscribed_event_ops

Just like with ctrl events, drivers may want to get called back on
listener add / remove for other event types too. Rather then special
casing all of this in subscribe / unsubscribe event it is better to
use ops for this.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/video/ivtv/ivtv-ioctl.c b/drivers/media/video/ivtv/ivtv-ioctl.c
index a151271..a7730fd 100644
--- a/drivers/media/video/ivtv/ivtv-ioctl.c
+++ b/drivers/media/video/ivtv/ivtv-ioctl.c
@@ -1469,7 +1469,7 @@
 	case V4L2_EVENT_VSYNC:
 	case V4L2_EVENT_EOS:
 	case V4L2_EVENT_CTRL:
-		return v4l2_event_subscribe(fh, sub, 0);
+		return v4l2_event_subscribe(fh, sub, 0, NULL);
 	default:
 		return -EINVAL;
 	}