V4L/DVB (9368): VBI fix for cx88 cards

The attached patch fix VBI support cx88 card.
I'm running a capture for hours, getting the closed caption from it[1], and
it's working perfect - the output is the same of a bttv card.
Please apply this patch as soon as possible.

[1] - using zvbi-ntsc-cc of zvbi project.

Signed-off-by: Rafael Diniz <diniz@wimobilis.com.br>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>