Fix a bug of streaming_tts_server (#3865)

* Fix a bug of streaming_tts_server

Fix "Failed to get model related files" when using fastspeech2_csmsc_onnx model in streaming_tts_server.

* Fix CodeStyle

paddlespeech/server/engine/tts/online/onnx/tts_engine.py

@@ -76,8 +76,8 @@ class TTSServerExecutor(TTSExecutor):
                     version=None,  # default version
                 )
                 self.am_res_path = self.task_resource.res_dir
-                self.am_ckpt = os.path.join(
-                    self.am_res_path, self.task_resource.res_dict['ckpt'][0])
+                self.am_ckpt = os.path.join(self.am_res_path,
+                                            self.task_resource.res_dict['ckpt'])
                 # must have phones_dict in acoustic
                 self.phones_dict = os.path.join(
                     self.am_res_path,