virtio_blk: use bvec_set_virt to initialize special_vec

Use the bvec_set_virt helper to initialize the special_vec.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20230203150634.3199647-10-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/virtio_blk.c

@@ -170,9 +170,7 @@ static int virtblk_setup_discard_write_zeroes_erase(struct request *req, bool un
 
 	WARN_ON_ONCE(n != segments);
 
-	req->special_vec.bv_page = virt_to_page(range);
-	req->special_vec.bv_offset = offset_in_page(range);
-	req->special_vec.bv_len = sizeof(*range) * segments;
+	bvec_set_virt(&req->special_vec, range, sizeof(*range) * segments);
 	req->rq_flags |= RQF_SPECIAL_PAYLOAD;
 
 	return 0;