cros flash: fix using non-standard image names

BUG=chromium:365126
TEST=`cros flash device path/to/local/image.bin`

Change-Id: Ia847941c388de388ba77e765d7dfddeddd10503b
Reviewed-on: https://chromium-review.googlesource.com/195825
Tested-by: Yu-Ju Hong <yjhong@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
1 file changed