[media] tvaudio: support V4L2_TUNER_MODE_LANG1_LANG2

Many of the audio decoders handled by the driver support this mode,
so the driver should support it as well.

Coding style errors are done to blend into the surrounding code.

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