Correctly report firmware update failure if RO needs update.

If the RO Firmware needs updating but can't be because it's
really RO, then report a new erro code (43) back to Omaha.

This normally only happens during board bringup when the RO
firmware is locked prematurely. We want to know these devices
exist so we can replace them.

BUG=chromium:218555
TEST=Build/unittests. Did NOT test on hardware with bug.

Change-Id: I383a999f1b175c378bef936c55d87565d8113336
Reviewed-on: https://gerrit.chromium.org/gerrit/63841
Commit-Queue: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
diff --git a/error_code.h b/error_code.h
index aab0917..65a5533 100644
--- a/error_code.h
+++ b/error_code.h
@@ -52,6 +52,7 @@
   kErrorCodeOmahaUpdateDeferredForBackoff = 40,
   kErrorCodePostinstallPowerwashError = 41,
   kErrorCodeUpdateCanceledByChannelChange = 42,
+  kErrorCodePostinstallFirmwareRONotUpdatable = 43,
 
   // Note: When adding new error codes, please remember to add the
   // error into one of the buckets in PayloadState::UpdateFailed method so