With the pktcdvdv removal, bio_copy_data_iter is unused now.  Fold the
logic into bio_copy_data and remove the separate lower level function.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221206144407.722049-1-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>