V4L/DVB (4380): Bttv: Revert VBI_OFFSET to previous value, it works better

A previous patch changed VBI_OFFSET to match what the datasheets say it
should be.  However, the bt8x8 datasheets are wrong.  The old value of
244 is closer to what is actually observed.  The real value appears to
not be constant and is different for different chip revisions.
Acked-by: Alan Cox <alan@redhat.com>

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>