futility: always create a tempfile in updater_apply_white_label()

Fix updater_apply_white_label() to not assume "<none>" is
a valid file path. Also remove a redundant duplication of
a error branch.

BUG=b:203715651
BRANCH=none
TEST=builds

Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Change-Id: I373d6fac4210e2055f9717e2266e9e2820c40f45
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/3295886
Tested-by: Edward O'Callaghan <quasisec@chromium.org>
Auto-Submit: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Edward O'Callaghan <quasisec@chromium.org>
1 file changed