drm/ast: remove unused validate_sequence

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ast/ast_drv.h

@@ -94,7 +94,6 @@ struct ast_private {
 		struct drm_global_reference mem_global_ref;
 		struct ttm_bo_global_ref bo_global_ref;
 		struct ttm_bo_device bdev;
-		atomic_t validate_sequence;
 	} ttm;
 
 	struct drm_gem_object *cursor_cache;