[media] tlg2300: allow multiple opens

Due to a poor administration of the driver state it wasn't possible to open
a video or vbi device multiple times.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>