drm/ttm: use ttm put pages function to properly restore cache attribute

On failure we need to make sure the page we free has wb cache
attribute. Do this pas call the proper ttm page helper function.
Signed-off-by: NJerome Glisse <jglisse@redhat.com>
Reviewed-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: NThomas Hellstrom <thellstrom@vmware.com>

drivers/gpu/drm/ttm/ttm_tt.c

@@ -90,7 +90,10 @@ static struct page *__ttm_tt_get_page(struct ttm_tt *ttm, int index)
 	}
 	return p;
 out_err:
-	put_page(p);
+	INIT_LIST_HEAD(&h);
+	list_add(&p->lru, &h);
+	ttm_put_pages(&h, 1, ttm->page_flags,
+		      ttm->caching_state, &ttm->dma_address[index]);
 	return NULL;
 }