check_ethernet.hook: fix lint warnings

Make sure variables are double quoted.

BUG=none
TEST=repo upload .

Change-Id: Ib4f819bd6eaf2798982607dd144ae51e53ccbfed
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/3985052
Commit-Queue: Grant Grundler <grundler@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Tested-by: Grant Grundler <grundler@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
1 file changed