falco: Fix HWID checksum

Random numbers apparently don't work here and will cause ChromeOS
to report an error on every boot of an official image.

BUG=chrome-os-partner:20235
BRANCH=none
TEST=manual: Boot on Falco without warning screen

Change-Id: I1b98fd82b6d47dd72f80b9039bfc62e956d1b7e3
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/59109
Reviewed-by: Aaron Durbin <adurbin@chromium.org>