[media] vb2: Allow queuing OUTPUT buffers with zeroed 'bytesused'

Modify the bytesused/data_offset check to not fail if both bytesused
and data_offset is set to 0. This should minimize possible issues in
existing applications which worked before we enforced the plane lengths
for output buffers checks introduced in commit 8023ed09
"videobuf2-core: Verify planes lengths for output buffers"

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>