Correct TopicMapper doc example (#1637)

Author: chrisji

bertopic/_bertopic.py

@@ -4030,7 +4030,7 @@ def get_mappings(self, original_topics: bool = True) -> Mapping[int, int]:
 
         To get mappings, simply call:
         ```python
-        mapper = TopicMapper(hdbscan_model)
+        mapper = TopicMapper(topics)
         mappings = mapper.get_mappings(original_topics=False)
         ```
         """