shim: fix a crash when reporting sign check failure

Cherry-pick commit[1] from the upstream with the fix for the
crash while reporting signature check failure, or any other failure
that is reported through VLogError function.

[1] https://github.com/rhboot/shim/commit/344a8364cb05cdaafc43231d0f73d5217c4e118c

BUG=b/176990752
TEST=presubmit
RELEASE_NOTE=None

Change-Id: I5f16af5e4ac768ed9066bfba66de3aeb42cc3753
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/14570
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
3 files changed