NFS: Assume cred is pinned by open context in I/O requests

In read/write/commit, we should be able to assume that the cred is
pinned by the open context.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/pagelist.c

@@ -627,7 +627,7 @@ int nfs_initiate_pgio(struct rpc_clnt *clnt, struct nfs_pgio_header *hdr,
 		.callback_ops = call_ops,
 		.callback_data = hdr,
 		.workqueue = nfsiod_workqueue,
-		.flags = RPC_TASK_ASYNC | flags,
+		.flags = RPC_TASK_ASYNC | RPC_TASK_CRED_NOREF | flags,
 	};
 	int ret = 0;