V4L/DVB (4729): Fix VIDIOC_G_FMT for NTSC in cx25840.

VIDIOC_G_FMT returned the sliced VBI types in the wrong lines for NTSC
(three lines too low).

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