minigbm/msm: Correct NV12 UBWC buffer allocation

minigbm/msm: Correct NV12 UBWC buffer allocation

V4L2 is the consumer of these buffers and sets up
the allocation in get_framesize_raw_nv12_ubwc().
There was a mismatch where V4L2 was aligning the
uv buffer differently than minigbm.

BUG=b:166157708
TEST=video_decode_accelerator_tests with 856x480 video

Change-Id: Idb9fb689a56639dbc73753d453e7e6e5daeb6700
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/2402146
Tested-by: Fritz Koenig <frkoenig@chromium.org>
Commit-Queue: Fritz Koenig <frkoenig@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>