SUNRPC: rpc_call_null_helper() already sets RPC_TASK_NULLCREDS

Clean up.

Commit a52458b4 ("NFS/NFSD/SUNRPC: replace generic creds with
'struct cred'.") made rpc_call_null_helper() set RPC_TASK_NULLCREDS
unconditionally. Therefore there's no need for
rpc_call_null_helper()'s call sites to set RPC_TASK_NULLCREDS.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/clnt.c

@@ -2816,7 +2816,7 @@ int rpc_clnt_test_and_add_xprt(struct rpc_clnt *clnt,
 	}
 
 	task = rpc_call_null_helper(clnt, xprt, NULL,
-			RPC_TASK_SOFT|RPC_TASK_SOFTCONN|RPC_TASK_ASYNC|RPC_TASK_NULLCREDS,
+			RPC_TASK_SOFT|RPC_TASK_SOFTCONN|RPC_TASK_ASYNC,
 			&rpc_cb_add_xprt_call_ops, data);
 
 	rpc_put_task(task);
@@ -2860,7 +2860,7 @@ int rpc_clnt_setup_test_and_add_xprt(struct rpc_clnt *clnt,
 
 	/* Test the connection */
 	task = rpc_call_null_helper(clnt, xprt, NULL,
-				    RPC_TASK_SOFT | RPC_TASK_SOFTCONN | RPC_TASK_NULLCREDS,
+				    RPC_TASK_SOFT | RPC_TASK_SOFTCONN,
 				    NULL, NULL);
 	if (IS_ERR(task)) {
 		status = PTR_ERR(task);