V4L/DVB (10444): cx18: Fix sliced VBI PTS and fix artifacts in last raw line of field

Fixed an endianess problem with the collection of the PTS from
the VBI buffer given to us by the encoder.  Also extrapolated the
last 12 bytes of the last line of each field, to remove artifacts
created by removing the first 12 bytes of each field for raw VBI.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>