drm/nouveau/ttm: don't dereference nvbo::cli, it can outlive client

Potentially responsible for some random OOPSes.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Cc: stable@vger.kernel.org [v4.15+]

drivers/gpu/drm/nouveau/nouveau_bo.h

@@ -26,8 +26,6 @@ struct nouveau_bo {
 
 	struct list_head vma_list;
 
-	struct nouveau_cli *cli;
-
 	unsigned contig:1;
 	unsigned page:5;
 	unsigned kind:8;