NFS: Fix uninitialized rpc_wait_queue

Michael Sterrett reports a NULL pointer dereference on NFSv3 mounts when
CONFIG_NFS_V4 is not set because the NFS UOC rpc_wait_queue has not been
initialized.  Move the initialization of the queue out of the CONFIG_NFS_V4
conditional setion.

Fixes: 7d6ddf88c4 ("NFS: Add an iocounter wait function for async RPC tasks")
Cc: stable@vger.kernel.org # 4.11+
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/client.c

@@ -218,7 +218,6 @@ static void nfs_cb_idr_remove_locked(struct nfs_client *clp)
 static void pnfs_init_server(struct nfs_server *server)
 {
 	rpc_init_wait_queue(&server->roc_rpcwaitq, "pNFS ROC");
-	rpc_init_wait_queue(&server->uoc_rpcwaitq, "NFS UOC");
 }
 
 #else
@@ -888,6 +887,7 @@ struct nfs_server *nfs_alloc_server(void)
 	ida_init(&server->openowner_id);
 	ida_init(&server->lockowner_id);
 	pnfs_init_server(server);
+	rpc_init_wait_queue(&server->uoc_rpcwaitq, "NFS UOC");
 
 	return server;
 }