V4L/DVB (9162): ivtv: fix raw/sliced VBI mixup

The service_set field was used in saa7115 and cx25840 to determine
whether raw or sliced VBI was desired. This is incorrect since it is
perfectly valid to select sliced VBI with a service_set of 0.

Instead these drivers should checked on VIDIOC_S_FMT whether the type
field matches the raw or sliced VBI type.

Updated ivtv accordingly.

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