svcrdma: fix error handling of rdma_alloc_frmr()

ib_alloc_fast_reg_mr() and ib_alloc_fast_reg_page_list() returns
ERR_PTR() and not NULL. Compile tested only.
Signed-off-by: NWei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>

net/sunrpc/xprtrdma/svc_rdma_transport.c

@@ -730,12 +730,12 @@ static struct svc_rdma_fastreg_mr *rdma_alloc_frmr(struct svcxprt_rdma *xprt)
 		goto err;
 
 	mr = ib_alloc_fast_reg_mr(xprt->sc_pd, RPCSVC_MAXPAGES);
-	if (!mr)
+	if (IS_ERR(mr))
 		goto err_free_frmr;
 
 	pl = ib_alloc_fast_reg_page_list(xprt->sc_cm_id->device,
 					 RPCSVC_MAXPAGES);
-	if (!pl)
+	if (IS_ERR(pl))
 		goto err_free_mr;
 
 	frmr->mr = mr;