io_uring: don't disable kiocb_done() CQE batching

Not passing issue_flags from kiocb_done() into __io_complete_rw() means
that completion batching for this case is disabled, e.g. for most of
buffered reads.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b2689462835c3ee28a5999ef4f9a581e24be04a2.1630539342.git.asml.silence@gmail.com


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