media: vivid: take data_offset into account for video output

The video output sizeimage calculation did not take data_offset into account.

This can cause problems with video loopback or exporting output buffers for
use as dmabuf import buffers since the output buffer size is now too small.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>