workqueue: use schedule_timeout_interruptible() instead of open code

schedule_timeout_interruptible(CREATE_COOLDOWN) is exactly the same as
the original code.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --cc kernel/workqueue.c
Simple merge