touch_updater: Fix presubmit errors in elan-hid-touch firmware script

Updated code to match recommended shell code best practices.

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

Change-Id: Ib666c5522e661f13ce2350c79e686ad169a696ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/touch_updater/+/4742837
Reviewed-by: Torsha Banerjee <torsha@google.com>
Auto-Submit: Henry Barnor <hbarnor@chromium.org>
Tested-by: Henry Barnor <hbarnor@chromium.org>
Reviewed-by: Kenneth Albanowski <kenalba@google.com>
Commit-Queue: Henry Barnor <hbarnor@chromium.org>
1 file changed