[media] au0828: Fix field alignment for video frames delivered by driver

Fix the alignment of fields being delivered by the driver, which was
resulting in jerky video when there was horizontal motion (since the bottom
field of the frame was being sent with the top field of the previous frame)

This work was sponsored by GetWellNetwork Inc.

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>