Fix: (issue #14127) Volc Engine MaaS import error (#14194)

- **Description:** fix Volc Engine MaaS import error
- **Issue:** [the issue # it fixes (if
applicable),](https://github.com/langchain-ai/langchain/issues/14127)
  - **Dependencies:** None
  - **Tag maintainer:** @baskaryan 
  - **Twitter handle:**

Co-authored-by: lvzhong <lvzhong@bytedance.com>

libs/langchain/langchain/llms/__init__.py

@@ -876,5 +876,5 @@ def get_type_to_cls_dict() -> Dict[str, Callable[[], Type[BaseLLM]]]:
         "javelin-ai-gateway": _import_javelin_ai_gateway,
         "qianfan_endpoint": _import_baidu_qianfan_endpoint,
         "yandex_gpt": _import_yandex_gpt,
-        "VolcEngineMaasLLM": _import_volcengine_maas(),
+        "VolcEngineMaasLLM": _import_volcengine_maas,
     }