workqueue: un-GPL function delayed_work_timer_fn()

commit 1438ade5 upstream.

commit d8e794df ("workqueue: set
delayed_work->timer function on initialization") exports function
delayed_work_timer_fn() only for GPL modules. This makes delayed-works
unusable for non-GPL modules, because initialization macro now requires
GPL symbol. For example schedule_delayed_work() available for non-GPL.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>