v4l2_stateful_decoder: Fix UV indices for top,left != 0

Fixes a problem when converting from NV12 to I420 when the visible area
has non-zero offset. The UV plane offsets need to be scaled down.

TEST=v4l2_stateful_decoder -f CONFWIN_A_Sony_1.hevc on trogdor

Change-Id: If1e05d056eb15c89ed023736e8b50fcbdaf10637
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/drm-tests/+/3570982
Tested-by: Nathan Hebert <nhebert@chromium.org>
Reviewed-by: Fritz Koenig <frkoenig@chromium.org>
Commit-Queue: Nathan Hebert <nhebert@chromium.org>
1 file changed