cxgb4: Fix error codes in c4iw_create_cq()

If one of these kmalloc() calls fails then we return ERR_PTR(0) which is
NULL.  It results in a NULL dereference in the callers.

Fixes: cfdda9d76436 ("RDMA/cxgb4: Add driver for Chelsio T4 RNIC")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/cxgb4/cq.c

@@ -963,6 +963,7 @@ struct ib_cq *c4iw_create_cq(struct ib_device *ibdev,
 		goto err3;
 
 	if (ucontext) {
+		ret = -ENOMEM;
 		mm = kmalloc(sizeof *mm, GFP_KERNEL);
 		if (!mm)
 			goto err4;