drm/nv50/dmaobj: extend class to allow gpu-specific attributes to be defined

disp is going to need to be able to create more specific dma objects
than was previously possible.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nouveau_abi16.c b/drivers/gpu/drm/nouveau/nouveau_abi16.c
index cc79c79..2720ce0 100644
--- a/drivers/gpu/drm/nouveau/nouveau_abi16.c
+++ b/drivers/gpu/drm/nouveau/nouveau_abi16.c
@@ -378,7 +378,7 @@
 	struct nouveau_abi16_chan *chan, *temp;
 	struct nouveau_abi16_ntfy *ntfy;
 	struct nouveau_object *object;
-	struct nv_dma_class args;
+	struct nv_dma_class args = {};
 	int ret;
 
 	if (unlikely(!abi16))