vboot: migrate GBB-related error handling to vboot2

Pass on values returned from vb2_gbb_* functions instead
of using VBERROR_INVALID_GBB on error.

BUG=b:124141368, chromium:988410
TEST=make clean && make runtests
BRANCH=none

Change-Id: I66b99393f0fcc9eabe629d08b35247764cfbcefb
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1728296
Tested-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
2 files changed