flashrom: set umask before creating temporary files

Good security practice.  Set to 077; resultant file permissions are:
  -rw-------

BUG=b:160717634
BRANCH=none
TEST=unit tests

Change-Id: Ib3b853c824be4c98e7b9ddd31797104ec4ab67a9
Signed-off-by: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2302962
Reviewed-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
2 files changed