Make tags always produces below annoying warnings:

ctags: Warning: kernel/workqueue.c:470: null expansion of name pattern "\1"
ctags: Warning: kernel/workqueue.c:474: null expansion of name pattern "\1"
ctags: Warning: kernel/workqueue.c:478: null expansion of name pattern "\1"

In commit 25528213 ("tags: Fix DEFINE_PER_CPU expansions"), codes in
places have been adjusted including cpu_worker_pools definition. I noticed
in commit 4cb1ef64 ("workqueue: Implement BH workqueues to eventually
replace tasklets"), cpu_worker_pools definition was unfolded back. Not
sure if it was intentionally done or ignored carelessly.

Makes change to mute them specifically.
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>