block: copy ioprio in __bio_clone_fast() and bounce

We need to copy the io priority, too; otherwise the clone will run
with a different priority than the original one.

Fixes: 43b62ce3

 ("block: move bio io prio to a new field")
Signed-off-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jean Delvare <jdelvare@suse.de>

Fixed up subject, and ordered stores.

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