Add ericrk@ to ui/gl OWNERS

Change-Id: I170282a5298026be223d63259cebd527444fb05a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1763159
Auto-Submit: Eric Karl <ericrk@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689106}

ui/gl/OWNERS

 backer@chromium.org
+ericrk@chromium.org
 kbr@chromium.org
 sunnyps@chromium.org
 zmo@chromium.org