Add myself to OWNERS for //storage.

Change-Id: Ib1ad967c2a331323b59f6bc40114f4a1a296eab4
Reviewed-on: https://chromium-review.googlesource.com/1148221
Commit-Queue: Joshua Bell <jsbell@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577588}

storage/OWNERS

 dmurph@chromium.org
 jsbell@chromium.org
+pwnall@chromium.org
 kinuko@chromium.org
 
 # TEAM: storage-dev@chromium.org