CI: Re-enable maintainer check

At this point we have all of the defconfigs maintained again, so
re-enable the check to prevent further regressions.

Signed-off-by: Tom Rini <trini@konsulko.com>

.gitlab-ci.yml

@@ -177,7 +177,7 @@ docs:
 Check for configs without MAINTAINERS entry:
   extends: .testsuites
   script:
-    - ./tools/buildman/buildman --maintainer-check || exit 0
+    - ./tools/buildman/buildman --maintainer-check
 
 # Ensure host tools build
 Build tools-only and envtools: