nouveau: init nvc0 channel alloc req structure fully

Kernel rejects ~0 handles, even though they're not used on NVC0.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/nouveau/abi16.c b/nouveau/abi16.c
index 688a9ac..0fa575c 100644
--- a/nouveau/abi16.c
+++ b/nouveau/abi16.c
@@ -55,7 +55,7 @@
 abi16_chan_nvc0(struct nouveau_object *obj)
 {
 	struct nouveau_device *dev = (struct nouveau_device *)obj->parent;
-	struct drm_nouveau_channel_alloc req;
+	struct drm_nouveau_channel_alloc req = {};
 	struct nvc0_fifo *nvc0 = obj->data;
 	int ret;