drm/ttm: stop pruning fences after wait

This is just abusing internals of the dma_resv object.
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20211129120659.1815-3-christian.koenig@amd.com

drivers/gpu/drm/ttm/ttm_bo.c

@@ -1086,7 +1086,6 @@ int ttm_bo_wait(struct ttm_buffer_object *bo,
 	if (timeout == 0)
 		return -EBUSY;
 
-	dma_resv_add_excl_fence(bo->base.resv, NULL);
 	return 0;
 }
 EXPORT_SYMBOL(ttm_bo_wait);