loop: aio inherit the ioprio of original request

Set cmd->iocb.ki_ioprio to the ioprio of loop device's request.
The purpose is to inherit the original request ioprio in the aio
flow.

Signed-off-by: Yunlong Xing <yunlong.xing@unisoc.com>
Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250414030159.501180-1-yunlong.xing@unisoc.com


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