media/gpu/OWNERS: bundle cros-specific and add mcasas@

Change-Id: Ie80c68ac5b4da0297f6dfe18c8a7f83da9cc8ddf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1779071Reviewed-by: Dan Sanders <sandersd@chromium.org>
Reviewed-by: Frank Liberato <liberato@chromium.org>
Reviewed-by: Kuang-che Wu <kcwu@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Auto-Submit: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692355}

media/gpu/OWNERS

-acourbot@chromium.org
 dalecurtis@chromium.org
 dcastagna@chromium.org
+liberato@chromium.org
+sandersd@chromium.org
+
+# For chromeos/, linux/, v4l2/, and vaapi/ -specific changes.
+acourbot@chromium.org
 hiroh@chromium.org
 jcliang@chromium.org
 kcwu@chromium.org
-liberato@chromium.org
+mcasas@chromium.org
 posciak@chromium.org
-sandersd@chromium.org