touch_updater: Fix presubmit errors in elan-touch firmware scripts

Updated code to match recommended shell code best practices. Only made
exception for `local` since though it is not POSIX complaint is
supported in most shells.

BUG=b:259595539
TEST=CQ
TEST=Deployed on Nightfury and used to downgrade+upgrade touch firmware

Change-Id: I0b97a949f87d4b9c902a6013f00cf12a9917c55c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/touch_updater/+/4742836
Auto-Submit: Henry Barnor <hbarnor@chromium.org>
Tested-by: Henry Barnor <hbarnor@chromium.org>
Commit-Queue: Henry Barnor <hbarnor@chromium.org>
Reviewed-by: Kenneth Albanowski <kenalba@google.com>
1 file changed