[media] tvaudio: use V4L2_TUNER_SUB_* for bitfields

The V4L2_TUNER_MODE_* constants are not suited for use in bitfields.

Signed-off-by: Daniel Glöckner <daniel-gl@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>