Fix calculating energy counter address

Author: brefra

plugwise/nodes/circle.py

@@ -813,7 +813,7 @@ def _energy_timestamp_memory_address(self, utc_timestamp: datetime):
         if utc_timestamp > _utc_now_timestamp:
             return None
 
-        _seconds_offset = _utc_now_timestamp.second
+        _seconds_offset = (_utc_now_timestamp - utc_timestamp).seconds
         _hours_offset = _seconds_offset / 3600
 
         _slot = self._energy_last_populated_slot