IB/mlx4: Handle -ENOMEM in forward_trap()

ib_create_send_mad() can return ERR_PTR(-ENOMEM) here.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mlx4/mad.c

@@ -211,6 +211,8 @@ static void forward_trap(struct mlx4_ib_dev *dev, u8 port_num, struct ib_mad *ma
 	if (agent) {
 		send_buf = ib_create_send_mad(agent, qpn, 0, 0, IB_MGMT_MAD_HDR,
 					      IB_MGMT_MAD_DATA, GFP_ATOMIC);
+		if (IS_ERR(send_buf))
+			return;
 		/*
 		 * We rely here on the fact that MLX QPs don't use the
 		 * address handle after the send is posted (this is