virtio_blk: use bvec_virt

Use bvec_virt instead of open coding it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Link: https://lore.kernel.org/r/20210804095634.460779-9-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/virtio_blk.c

@@ -166,11 +166,8 @@ static inline void virtblk_request_done(struct request *req)
 {
 	struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
 
-	if (req->rq_flags & RQF_SPECIAL_PAYLOAD) {
-		kfree(page_address(req->special_vec.bv_page) +
-		      req->special_vec.bv_offset);
-	}
-
+	if (req->rq_flags & RQF_SPECIAL_PAYLOAD)
+		kfree(bvec_virt(&req->special_vec));
 	blk_mq_end_request(req, virtblk_result(vbr));
 }