vboot: cgpt: fix my_lba of the secondary GPT

Previously, my_lba of the secondary GPT was recorded as if that
GPT was written at the end of the device. This patch tweaks
my_lba to report where it is in the random-access GPT address space,
namely at the end of that space.

TEST=Compiled it into the firmware and observed the firmware to update
the my_lba field of the secondary GPT.
BRANCH=none
BUG=chromium:425677

Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>

Change-Id: I88791fb2cff1086351ca8a3adeef675c4a88cc9a
Reviewed-on: https://chromium-review.googlesource.com/228942
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
Commit-Queue: Daniel Ehrenberg <dehrenberg@chromium.org>
Tested-by: Daniel Ehrenberg <dehrenberg@chromium.org>
6 files changed