CROS_OWNERS: add Michael

And allow us to self-service this file in the future.

Change-Id: I699480919bcb41250552123e691ddf1432077003
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2231900Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Michael Mortensen <mmortensen@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>

CROS_OWNERS

 # Chrome OS developers looking over Chrome OS related files.
 cjmcdonald@chromium.org
 lamontjones@chromium.org
+mmortensen@google.com
 nednguyen@chromium.org
 saklein@chromium.org
 vapier@chromium.org

OWNERS

@@ -22,6 +22,7 @@ per-file chrome_set_ver=file://CROS_OWNERS
 per-file cros=file://CROS_OWNERS
 per-file cros_sdk=file://CROS_OWNERS
 per-file repo=file://CROS_OWNERS
+per-file CROS_OWNERS=file://CROS_OWNERS
 
 # for the Goma client update
 per-file cipd_manifest*=file://GOMA_OWNERS