common.sh: adapt to get clean shellcheck

BUG=chromium:1141907
TEST=unit tests and manual signing run
Signed-off-by: George Engelbrecht <engeg@google.com>
BRANCH=none

Change-Id: I39b133ca69e717576140b418fc59dd167f068d59
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2514558
Reviewed-by: Sean McAllister <smcallis@google.com>
Reviewed-by: LaMont Jones <lamontjones@chromium.org>
Commit-Queue: George Engelbrecht <engeg@google.com>
Tested-by: George Engelbrecht <engeg@google.com>
2 files changed