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_user.h b/arch/um/drivers/chan_user.h
index dc693298..03f1b56 100644
--- a/arch/um/drivers/chan_user.h
+++ b/arch/um/drivers/chan_user.h
@@ -38,10 +38,10 @@
 			       unsigned short *cols_out);
 extern void generic_free(void *data);
 
-struct tty_struct;
-extern void register_winch(int fd,  struct tty_struct *tty);
+struct tty_port;
+extern void register_winch(int fd,  struct tty_port *port);
 extern void register_winch_irq(int fd, int tty_fd, int pid,
-			       struct tty_struct *tty, unsigned long stack);
+			       struct tty_port *port, unsigned long stack);
 
 #define __channel_help(fn, prefix) \
 __uml_help(fn, prefix "[0-9]*=<channel description>\n" \