[media] ivtv: remove open_id/id from the filehandle code

Instead of messing around with id's it's much easier to just compare
against a filehandle pointer.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>