workqueue: sanity check pool->cpu in wq_worker_sleeping()

In theory, pool->cpu is equals to @cpu in wq_worker_sleeping() after
worker->flags is checked.

And "pool->cpu != cpu" sanity check will help us if something wrong.

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

Original commit: https://github.com/mythos234/SimplKernel-LL-G925F/commit/914712648fc5f8e53b700dc373c8b267aa6f070e