media: bttv: use audio defaults for winfast2000

The winfast2000 card advertised rxsubchans that weren't compatible with
its default audmode. Just use the default audmode (V4L2_TUNER_MODE_MONO)
and default audio reception flag (V4L2_TUNER_SUB_MONO) for this card.
Fixes compliance test failures.

Signed-off-by: Deborah Brouwer <deborah.brouwer@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>