Add beccahughes to ash/media/OWNERS

Bug: none
Change-Id: Icf58036bec43cd560ca8119428bcf6b5d2e17004
Reviewed-on: https://chromium-review.googlesource.com/c/1367656Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614731}

ash/media/OWNERS

+beccahughes@chromium.org