io-wq: don't repeat IO_WQ_BIT_EXIT check by worker

io_wqe_worker()'s main loop does check IO_WQ_BIT_EXIT flag, so no need
for a second test_bit at the end as it will immediately jump to the
first check afterwards.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d6af4a51c86523a527fb5417c9fbc775c4b26497.1623634181.git.asml.silence@gmail.com


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