io_uring: make io_fill_cqe_aux static

This is only used in io_uring.c

Signed-off-by: Dylan Yudaken <dylany@meta.com>
Link: https://lore.kernel.org/r/20221124093559.3780686-7-dylany@meta.com


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