istallion: Use helpers

The ldisc needs to be referenced properly when used. The tty layer has a
helper for this which should have been used but this driver got missed
originally.
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/istallion.c

@@ -925,8 +925,7 @@ static void stli_close(struct tty_struct *tty, struct file *filp)
 	clear_bit(ST_TXBUSY, &portp->state);
 	clear_bit(ST_RXSTOP, &portp->state);
 	set_bit(TTY_IO_ERROR, &tty->flags);
-	if (tty->ldisc.ops->flush_buffer)
-		(tty->ldisc.ops->flush_buffer)(tty);
+	tty_ldisc_flush(tty);
 	set_bit(ST_DOFLUSHRX, &portp->state);
 	stli_flushbuffer(tty);