workqueue: Remove the argument @cpu_going_down from wq_calc_pod_cpumask()

wq_calc_pod_cpumask() uses wq_online_cpumask, which excludes the cpu
going down, so the argument cpu_going_down is unused and can be removed.

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