drm/nouveau/fifo: audit and version fifo channel classes

The full object interfaces are about to be exposed to userspace, so we
need to check for any security-related issues and version the structs
to make it easier to handle any changes we may need in the future.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nv50_display.c b/drivers/gpu/drm/nouveau/nv50_display.c
index 5e033b6..4f50add 100644
--- a/drivers/gpu/drm/nouveau/nv50_display.c
+++ b/drivers/gpu/drm/nouveau/nv50_display.c
@@ -410,7 +410,7 @@
 	if (unlikely(push == NULL))
 		return -EBUSY;
 
-	if (chan && chan->object->oclass < NV84_CHANNEL_IND_CLASS) {
+	if (chan && chan->object->oclass < G82_CHANNEL_GPFIFO) {
 		ret = RING_SPACE(chan, 8);
 		if (ret)
 			return ret;
@@ -424,7 +424,7 @@
 		OUT_RING  (chan, sync->addr);
 		OUT_RING  (chan, sync->data);
 	} else
-	if (chan && chan->object->oclass < NVC0_CHANNEL_IND_CLASS) {
+	if (chan && chan->object->oclass < FERMI_CHANNEL_GPFIFO) {
 		u64 addr = nv84_fence_crtc(chan, nv_crtc->index) + sync->addr;
 		ret = RING_SPACE(chan, 12);
 		if (ret)