V4L/DVB: cx25840: support new vbi ops to set/get VBI format

Also removed the bogus zeroing of fmt.sliced when setting up raw VBI.

Switching between raw and sliced VBI changed in 2.6.28 and this memset
should have been removed at that time. It was never noticed because
the bridge driver will fill in the fmt.vbi values anyway.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>