Fix for cppcheck warning about uninitialised data member
The new cpp_check
nightlies reported the following warning in MdtCalibT0
/build/atnight/localbuilds/nightlies/Athena/main--cppcheck/athena/MuonSpectrometer/MuonCalib/MdtCalib/MdtCalibT0/MdtCalibT0/ADCMTHistos.h:48:16: warning: Member variable 'ADCMTHistos::m_settings' is not initialized in the constructor. [uninitMemberVar]
inline ADCMTHistos() : m_adc(NULL), m_id(-1), m_adc_ok(false) {}