mod_image_for_recovery: don't require $USE to be set

BUG=none
TEST=ran script without setting $USE

Change-Id: I830d79c4fc6bfdeb097195be6c866f6c57149256
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3551279
Tested-by: Paramjit Oberoi <psoberoi@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed