drm/nv50/fb: fix double free of vram mm

nouveau_fb_destroy already calls nouveau_mm_fini on vram mm.
Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/core/subdev/fb/nv50.c

@@ -277,7 +277,6 @@ nv50_fb_dtor(struct nouveau_object *object)
 		__free_page(priv->r100c08_page);
 	}
 
-	nouveau_mm_fini(&priv->base.vram);
 	nouveau_fb_destroy(&priv->base);
 }