RDMA/iwcm: Test rdma_create_id() for IS_ERR rather than 0

The function rdma_create_id() always returns either a valid pointer or
a value made with ERR_PTR, so its result should be tested with IS_ERR,
not with a test for 0.

The problem was found using the following semantic match.
(http://www.emn.fr/x-info/coccinelle/)

//<smpl>
@a@
expression E, E1;
statement S,S1;
position p;
@@

E = rdma_create_id(...)
... when != E = E1
if@p (E) S else S1

@n@
position a.p;
expression E,E1;
statement S,S1;
@@

E = NULL
... when != E = E1
if@p (E) S else S1

@depends on !n@
expression E;
statement S,S1;
position a.p;
@@

* if@p (E)
  S else S1
//</smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/core/cma.c

@@ -1289,7 +1289,7 @@ static int iw_conn_req_handler(struct iw_cm_id *cm_id,
 	new_cm_id = rdma_create_id(listen_id->id.event_handler,
 				   listen_id->id.context,
 				   RDMA_PS_TCP);
-	if (!new_cm_id) {
+	if (IS_ERR(new_cm_id)) {
 		ret = -ENOMEM;
 		goto out;
 	}