workqueue: add myself as a dedicated reviwer

I am one of the dedicated reviwers of workqueue.c. Now I add myself
to the MAINTAINERS entry with the updated email address.

The old laijs@cn.fujitsu.com will be ended soon.

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