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>
diff --git a/arch/um/drivers/chan.h b/arch/um/drivers/chan.h
index 78f1b89..c512b03 100644
--- a/arch/um/drivers/chan.h
+++ b/arch/um/drivers/chan.h
@@ -37,7 +37,7 @@
 extern int console_open_chan(struct line *line, struct console *co);
 extern void deactivate_chan(struct chan *chan, int irq);
 extern void reactivate_chan(struct chan *chan, int irq);
-extern void chan_enable_winch(struct chan *chan, struct tty_struct *tty);
+extern void chan_enable_winch(struct chan *chan, struct tty_port *port);
 extern int enable_chan(struct line *line);
 extern void close_chan(struct line *line);
 extern int chan_window_size(struct line *line,