nvme: use bvec_virt

Use bvec_virt instead of open coding it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20210804095634.460779-16-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/host/core.c

@@ -968,12 +968,11 @@ void nvme_cleanup_cmd(struct request *req)
 {
 	if (req->rq_flags & RQF_SPECIAL_PAYLOAD) {
 		struct nvme_ctrl *ctrl = nvme_req(req)->ctrl;
-		struct page *page = req->special_vec.bv_page;
 
-		if (page == ctrl->discard_page)
+		if (req->special_vec.bv_page == ctrl->discard_page)
 			clear_bit_unlock(0, &ctrl->discard_page_busy);
 		else
-			kfree(page_address(page) + req->special_vec.bv_offset);
+			kfree(bvec_virt(&req->special_vec));
 	}
 }
 EXPORT_SYMBOL_GPL(nvme_cleanup_cmd);