unify queue_delayed_work() and queue_delayed_work_on()

Change queue_delayed_work() to use queue_delayed_work_on() to avoid the code
duplication (saves 133 bytes).

Q: queue_delayed_work() enqueues &dwork->work directly when delay == 0, why?

[jirislaby@gmail.com: oops fix]
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>