sunrpc: xprtrdma: Use ERR_CAST() to return

Using ERR_CAST() is more reasonable and safer, When it is necessary
to convert the type of an error pointer and return it.
Signed-off-by: Yan Zhen <yanzhen@vivo.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/xprtrdma/svc_rdma_transport.c

@@ -369,7 +369,7 @@ static struct svc_xprt *svc_rdma_create(struct svc_serv *serv,
 	listen_id = svc_rdma_create_listen_id(net, sa, cma_xprt);
 	if (IS_ERR(listen_id)) {
 		kfree(cma_xprt);
-		return (struct svc_xprt *)listen_id;
+		return ERR_CAST(listen_id);
 	}
 	cma_xprt->sc_cm_id = listen_id;