This is needed temporarily until we also update the MuonDetLayerGeometry. The problem is the code assumes MuonDetLayerGeometry and the base class agree on the type. However MuonDetLayerGeometry is using a ```std::vector<DetLayer*>``` while the base class is now using ```std::vector<const DetLayer*>```. The two have the same binary layout so the conversion, although strange, is OK.