[media] v4l2-event: Deny subscribing with a type of V4L2_EVENT_ALL

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>