x25_asy: Fix ref count rule violation

x25_asy does not take an ldisc reference before calling the flush method.
Fix it to use the helper function we provide.

Signed-off-by: Alan Cox <[e-mail]>
Cc: Krzysztof Halasa <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Cc: Jeff Garzik <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/net/wan/x25_asy.c

···
 static int x25_asy_open_tty(struct tty_struct *tty)
 {
 	struct x25_asy *sl = (struct x25_asy *) tty->disc_data;
+	struct tty_ldisc *ld;
 	int err;
 
 	/* First make sure we're not already connected. */
···
 	if (tty->driver->flush_buffer)  {
 		tty->driver->flush_buffer(tty);
 	}
-	if (tty->ldisc.flush_buffer)  {
-		tty->ldisc.flush_buffer(tty);
-	}
+	tty_ldisc_flush(tty);
 
 	/* Restore default settings */
 	sl->dev->type = ARPHRD_X25;