util/ec_flash: avoid divide-by-zero
util/ec_flash: avoid divide-by-zero

BUG=none
BRANCH=none
TEST=none

Change-Id: I514c2aa307e94be826e9c8e219eb471892b3fad6
Signed-off-by: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@google.com>
Found-by: Coverity Scan #201954
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1725951
Tested-by: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>
Auto-Submit: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>
Reviewed-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Commit-Queue: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec