um: Use tty_port in SIGWINCH handler

The tty below tty_port might get destroyed by the tty layer
while we hold a reference to it.
So we have to carry tty_port around...

Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/drivers/chan_kern.c

@@ -122,10 +122,10 @@ static int open_chan(struct list_head *chans)
 	return err;
 }
 
-void chan_enable_winch(struct chan *chan, struct tty_struct *tty)
+void chan_enable_winch(struct chan *chan, struct tty_port *port)
 {
 	if (chan && chan->primary && chan->ops->winch)
-		register_winch(chan->fd, tty);
+		register_winch(chan->fd, port);
 }
 
 static void line_timer_cb(struct work_struct *work)