io_uring: move min_events sanitisation

iopoll and normal waiting already duplicate min_completion truncation,
so move them inside the corresponding routines.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/254adb289cc04638f25d746a7499260fa89a179e.1742829388.git.asml.silence@gmail.com


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