block: remove blk_rq_bio_prep

There is not real point in a helper just to assign three values to four
fields, especially when the surrounding code is working on the
neighbor fields directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Link: https://lore.kernel.org/r/20250103073417.459715-3-hch@lst.de


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