crossystem: use wpsw_boot as fallback for wpsw_cur

In preparation for deprecating wpsw_boot, update wpsw_cur
to use wpsw_boot as a fallback value.

The source of wpsw_boot will still be deprecated on devices
using new firmware, but in those cases, we are absolutely
certain that wpsw_cur will work.

BUG=b:124141368, chromium:950723
TEST=make clean && make runtests
BRANCH=none

Change-Id: I77ab9c6b827ef2c033ae46b7b01b12465101c0a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2071633
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
2 files changed