ubd: use bvec_virt

Use bvec_virt instead of open coding it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Link: https://lore.kernel.org/r/20210804095634.460779-12-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

arch/um/drivers/ubd_kern.c

@@ -1268,8 +1268,7 @@ static void ubd_map_req(struct ubd *dev, struct io_thread_req *io_req,
 		rq_for_each_segment(bvec, req, iter) {
 			BUG_ON(i >= io_req->desc_cnt);
 
-			io_req->io_desc[i].buffer =
-				page_address(bvec.bv_page) + bvec.bv_offset;
+			io_req->io_desc[i].buffer = bvec_virt(&bvec);
 			io_req->io_desc[i].length = bvec.bv_len;
 			i++;
 		}