TTY: switch tty_insert_flip_string

Now, we start converting tty buffer functions to actually use
tty_port. This will allow us to get rid of the need of tty in many
call sites. Only tty_port will needed and hence no more
tty_port_tty_get in those paths.

tty_insert_flip_string this time.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/isdn/gigaset/interface.c b/drivers/isdn/gigaset/interface.c
index 67abf3f..dd2a57e 100644
--- a/drivers/isdn/gigaset/interface.c
+++ b/drivers/isdn/gigaset/interface.c
@@ -569,7 +569,7 @@
 		return;
 	}
 
-	tty_insert_flip_string(tty, buffer, len);
+	tty_insert_flip_string(&cs->port, buffer, len);
 	tty_flip_buffer_push(tty);
 	tty_kref_put(tty);
 }