io-wq: cancel task_work on exit only targeting the current 'wq'

With using task_work_cancel(), we're potentially canceling task_work
that isn't related to this specific io_wq. Use the newly added
task_work_cancel_match() to ensure that we only remove and cancel work
items that are specific to this io_wq.

Fixes: 685fe7fe ("io-wq: eliminate the need for a manager thread")
Signed-off-by: Jens Axboe <axboe@kernel.dk>