io_uring/napi: Remove unnecessary s64 cast

Since the do_div() macro casts the divisor to u32 anyway, remove the
unnecessary s64 cast and fix the following Coccinelle/coccicheck
warning reported by do_div.cocci:

  WARNING: do_div() does a 64-by-32 division, please consider using div64_s64 instead

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Link: https://lore.kernel.org/r/20240710010520.384009-2-thorsten.blum@toblux.com


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