IB/hfi1: checking for NULL instead of IS_ERR

__get_txreq() returns an ERR_PTR() but this checks for NULL so it would
oops on failure.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/staging/rdma/hfi1/verbs.c

@@ -749,10 +749,12 @@ static inline struct verbs_txreq *get_txreq(struct hfi1_ibdev *dev,
 	struct verbs_txreq *tx;
 
 	tx = kmem_cache_alloc(dev->verbs_txreq_cache, GFP_ATOMIC);
-	if (!tx)
+	if (!tx) {
 		/* call slow path to get the lock */
 		tx =  __get_txreq(dev, qp);
-	if (tx)
+		if (IS_ERR(tx))
+			return tx;
+	}
 	tx->qp = qp;
 	return tx;
 }