firmware: Prevent wraparound when scrolling through menus
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 <ab7b8cc85923339aed379eb1c5cc4dccfd2eb3d7@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/426410
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot