Add hirokisato to OWNERS of c/b/c/arc/accessibility

Bug: None
Test: None
Change-Id: I7a60ef70621e52670c508b72aaf499d5f787551d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1978396Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727154}

chrome/browser/chromeos/arc/accessibility/OWNERS

 dtseng@chromium.org
+hirokisato@chromium.org
 sarakato@chromium.org
 
 file://ui/accessibility/OWNERS