TTY: pty, fix tty buffers leak

After commit "TTY: move tty buffers to tty_port", the tty buffers are
not freed in some drivers. This is because tty_port_destructor is not
called whenever a tty_port is freed. This was an assumption I counted
with but was unfortunately untrue. So fix the drivers to fulfil this
assumption.

PTY is one of those, here we just need to use tty_port_put instead of
kfree. (Assuming tty_port_destructor does not need port->ops to be set
which we change here too.)
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -408,7 +408,7 @@ static void pty_unix98_shutdown(struct tty_struct *tty)
 static void pty_cleanup(struct tty_struct *tty)
 {
 	tty->port->itty = NULL;
-	kfree(tty->port);
+	tty_port_put(tty->port);
 }
 
 /* Traditional BSD devices */

drivers/tty/tty_port.c

@@ -128,7 +128,7 @@ static void tty_port_destructor(struct kref *kref)
 	if (port->xmit_buf)
 		free_page((unsigned long)port->xmit_buf);
 	tty_buffer_free_all(port);
-	if (port->ops->destruct)
+	if (port->ops && port->ops->destruct)
 		port->ops->destruct(port);
 	else
 		kfree(port);