io_uring: store add. return values for CQE32

This reuses the hash list node for the storage we need to hold the two
64-bit values that must be passed back.

Co-developed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Stefan Roesch <shr@fb.com>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Link: https://lore.kernel.org/r/20220426182134.136504-3-shr@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>