io-wq: simplify worker exiting

io_worker_handle_work() already takes care of the empty list case and
releases spinlock, so get rid of ugly conditional unlocking and
unconditionally call handle_work()

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/7521e485677f381036676943e876a0afecc23017.1623634181.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>