io_uring: don't propagate io_comp_state

There is no reason to drag io_comp_state into opcode handlers, we just
need a flag and the actual work will be done in __io_queue_sqe().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>