fix paddlepredictor build error. test=develop (#28792)

paddle/fluid/inference/lite/engine.cc

@@ -53,7 +53,7 @@ paddle::lite_api::PaddlePredictor* EngineManager::Create(
                                    cfg.param.c_str(), cfg.param.size());
   lite_cxx_config.set_valid_places(cfg.valid_places);
 #ifdef PADDLE_WITH_ARM
-  set_threads.set_threads(cfg.cpu_math_library_num_threads);
+  lite_cxx_config.set_threads(cfg.cpu_math_library_num_threads);
 #else
   lite_cxx_config.set_x86_math_library_num_threads(
       cfg.cpu_math_library_num_threads);