Correct OPC-UA call syntax to close_secure_channel()

StatsCrosslet-DS/StatsCrosslet.py

@@ -210,7 +210,7 @@ class StatsCrosslet(Device):
         self.debug_stream("Waiting for data acquisition thread to shut down, done")
         if self.client is not None:
             self.client.close_session()
-            self.client_secure_channel()
+            self.client.close_secure_channel()
         self.debug_stream("Shutdown done.")
         # PROTECTED REGION END #    //  StatsCrosslet.delete_device
     # ------------------