We can't use RQF_DONTPREP to see if we should clear ->special,
as someone could have set that while inserting the request. Make
sure we clear it in our ->initialize_rq_fn() helper instead.

Fixes: 22ce0a7c ("ide: don't use req->special")
Signed-off-by: Jens Axboe <axboe@kernel.dk>