nvme: refactor ns->ctrl by request

Just for current code in nvme_cleanup_cmd(), we don't have to get
namespace instance, but we need controller instance.

Controller instance can be retrieved by namespace instance, but it can
be directly accessed by nvme_request instance from request.

	ctrl = nvme_req(req)->ctrl;

We don't have to go around namespace instance from request instance
through gendisk.

Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -841,11 +841,11 @@ static inline blk_status_t nvme_setup_rw(struct nvme_ns *ns,
 void nvme_cleanup_cmd(struct request *req)
 {
 	if (req->rq_flags & RQF_SPECIAL_PAYLOAD) {
-		struct nvme_ns *ns = req->rq_disk->private_data;
+		struct nvme_ctrl *ctrl = nvme_req(req)->ctrl;
 		struct page *page = req->special_vec.bv_page;
 
-		if (page == ns->ctrl->discard_page)
-			clear_bit_unlock(0, &ns->ctrl->discard_page_busy);
+		if (page == ctrl->discard_page)
+			clear_bit_unlock(0, &ctrl->discard_page_busy);
 		else
 			kfree(page_address(page) + req->special_vec.bv_offset);
 	}