io-wq: simplify code in __io_worker_busy()

Leverage XOR to simplify the code in __io_worker_busy.

Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
Link: https://lore.kernel.org/r/1617678525-3129-1-git-send-email-haoxu@linux.alibaba.com


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