IB/mthca: Handle -ENOMEM in forward_trap()

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

drivers/infiniband/hw/mthca/mthca_mad.c

@@ -171,6 +171,8 @@ static void forward_trap(struct mthca_dev *dev,
 	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