workqueue: Don't bind the rescuer in the last working cpu

So that when the rescuer is woken up next time, it will not interrupt
the last working cpu which might be busy on other crucial works but
have nothing to do with the rescuer's incoming works.

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