drm/nouveau: Fix notifier blocks over the 4GB mark.

Signed-off-by: Francisco Jerez <[e-mail]>
Signed-off-by: Ben Skeggs <[e-mail]>

drivers/gpu/drm/nouveau/nouveau_notifier.c

···
 	struct drm_nouveau_private *dev_priv = dev->dev_private;
 	struct nouveau_gpuobj *nobj = NULL;
 	struct drm_mm_node *mem;
-	uint32_t offset;
+	uint64_t offset;
 	int target, ret;
 
 	mem = drm_mm_search_free_in_range(&chan->notifier_heap, size, 0,