tty: use the new 'flush_delayed_work()' helper to do ldisc flush

This way all flush_to_ldisc work is always done through the workqueues,
and we thus have a single point of serialization.

Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/tty_buffer.c

···
  */
 void tty_flush_to_ldisc(struct tty_struct *tty)
 {
-	flush_to_ldisc(&tty->buf.work.work);
+	flush_delayed_work(&tty->buf.work);
 }
 
 /**