Fix typo in rfc3961 namespace-cleaning

Change-Id: If93119ce4345ab8d1eccb9df7196b1681d2762cb
Reviewed-on: http://gerrit.openafs.org/10550
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>