lxc: do cleanup when failed to bind fs as read-only

We forgot to do cleanup when lxcContainerMountFSTmpfs
failed to bind fs as read-only.

Signed-off-by: Chen Hanxiao <chenhanxiao@cn.fujitsu.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

src/lxc/lxc_container.c

@@ -1451,6 +1451,7 @@ static int lxcContainerMountFSTmpfs(virDomainFSDefPtr fs,
             virReportSystemError(errno,
                                  _("Failed to make directory %s readonly"),
                                  fs->dst);
+            goto cleanup;
         }
     }