Revert "workqueue: remove unused cancel_work()"

[ Upstream commit 73b4b532 ]

This reverts commit 6417250d.

amdpgu need this function in order to prematurly stop pending
reset works when another reset work already in progress.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Lai <Jiangshan&lt;jiangshanlai@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Stable-dep-of: 91d3d149 ("r8169: prevent potential deadlock in rtl8169_close")
Signed-off-by: Sasha Levin <sashal@kernel.org>