NFS: Don't cleanup sysfs superblock entry if uninitialized

Its possible to end up in nfs_free_server() before the server's superblock
sysfs entry has been initialized, in which case calling kobject_put() will
emit a WARNING.  Check if the kobject has been initialized before cleaning
it up.

Fixes: 1c7251187d ("NFS: add superblock sysfs entries")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/client.c

@@ -1021,8 +1021,10 @@ void nfs_free_server(struct nfs_server *server)
 
 	nfs_put_client(server->nfs_client);
 
-	nfs_sysfs_remove_server(server);
-	kobject_put(&server->kobj);
+	if (server->kobj.state_initialized) {
+		nfs_sysfs_remove_server(server);
+		kobject_put(&server->kobj);
+	}
 	ida_free(&s_sysfs_ids, server->s_sysfs_id);
 
 	ida_destroy(&server->lockowner_id);