RDMA/cxgb4: Don't use null ep ptr

In c4iw_modify_qp() error path, only use qhp->ep if ep is not already set.
Otherwise qhp->ep can be NULL and we crash.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/cxgb4/qp.c

@@ -1305,7 +1305,8 @@ err:
 
 	/* disassociate the LLP connection */
 	qhp->attr.llp_stream_handle = NULL;
-	ep = qhp->ep;
+	if (!ep)
+		ep = qhp->ep;
 	qhp->ep = NULL;
 	qhp->attr.state = C4IW_QP_STATE_ERROR;
 	free = 1;