workqueue: Remove the arguments @hotplug_cpu and @online from wq_update_pod()

The arguments @hotplug_cpu and @online are not used in wq_update_pod()
since the functions called by wq_update_pod() don't need them.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Tejun Heo <tj@kernel.org>