Replace %llu by PRIu64 in AIO io_uring code

Replace %llu by PRIu64 in AIO io_uring code

This is a continuation of 15a79c73111f, cleaning up the AIO io_uring
code that has been committed after that while still using %llu.

The code changed here is new in v18, so cleaning things now means less
conflicts if this area of the code changes on backpatch once the 18
stable branch is created.

Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: http://postgr.es/m/aEZcGCnYFq642q8k@paquier.xyz