media/gpu: add frkoenig@ as Chrome OS owner

frkoenig@ is one of the main owners of the Chrome OS/V4L2
parts. Add him to the OWNERS file.

BUG=None
TEST=None

Change-Id: I53a3e3cf5816f7ae7ca529fcdf7de153d5a0e2ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2260095
Commit-Queue: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Fritz Koenig <frkoenig@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781426}

media/gpu/OWNERS

@@ -5,6 +5,7 @@ sandersd@chromium.org
 
 # For chromeos/, linux/, v4l2/, and vaapi/ -specific changes.
 acourbot@chromium.org
+frkoenig@chromium.org
 hiroh@chromium.org
 jcliang@chromium.org
 jkardatzke@chromium.org