zephyr: config check script cleanup
zephyr: config check script cleanup

This fixes the tmp file cleanup logic. We use "mktemp -d" to create a
temporary directory, but then use this name as the basename for tmp
files instead of path prefix. So, use '/' instead of '.' to compose tmp
file paths.

BRANCH=none
BUG=none
TEST=/tmp is no longer polluted with stale tmp files

Change-Id: I585c39065d71a39edc6d333b34f157fe27d2b511
Signed-off-by: Caveh Jalali <08e24a66aefda7a55ca7d73f8903e0fb16eec763@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2771742
Reviewed-by: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec