gbb_flags_common.sh: Restore tmpfile cleanup trap

A trap to delete tempfiles was mistakenly masked.

BUG=b:247920664
BRANCH=None
TEST=get_gbb_flags.sh; ls /tmp/tmp.* | wc -l == 0

Change-Id: I3b783395309ea2acb1bc75ffa19df62f81b90450
Signed-off-by: Evan Benn <evanbenn@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/3907130
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
Commit-Queue: Yu-Ping Wu <yupingso@chromium.org>

scripts/image_signing/gbb_flags_common.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 #
-# Copyright 2017 The Chromium OS Authors. All rights reserved.
+# Copyright 2017 The ChromiumOS Authors
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
@@ -73,7 +73,10 @@ maybe_disable_cpu_fw_spi() {
   if [ "${CPU_FW_SPI}" = "${FLAGS_TRUE}" ]; then
     dut-control cpu_fw_spi:off >/dev/null
   fi
+  cleanup_temps_and_mounts
 }
+
+# This overrides the trap set in common_minimal.
 trap "maybe_disable_cpu_fw_spi" EXIT
 
 update_programmer_for_servo() {