tty: serial - fix tty referencing in set_ldisc

Pass down the ldisc number so that the drivers don't have to peek into the
tty object themselves. This lets us get rid of another case of back referencing
port to tty which we don't want (because of races versus hangup/close).

Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index f10db6e..32928161 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -220,7 +220,7 @@
 	void		(*flush_buffer)(struct uart_port *);
 	void		(*set_termios)(struct uart_port *, struct ktermios *new,
 				       struct ktermios *old);
-	void		(*set_ldisc)(struct uart_port *);
+	void		(*set_ldisc)(struct uart_port *, int new);
 	void		(*pm)(struct uart_port *, unsigned int state,
 			      unsigned int oldstate);
 	int		(*set_wake)(struct uart_port *, unsigned int state);