firmware: Prevent wraparound when scrolling through menus

BUG=chrome-os-partner:61275
BRANCH=None
TEST=reboot and scroll to ends of menus to make sure that
     they don't wraparound.

Change-Id: I9ba83b23939140d23fe54858b9a10f873091ff72
Signed-off-by: Shelley Chen <shchen@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/426410
Reviewed-by: Randall Spangler <rspangler@chromium.org>
1 file changed