[media] media: au0828 VBI support comment cleanup

This driver supports VBI and the comment "VBI support
is not yet working" is inaccurate. Remove it.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>