Fixing the strip identifier in the MM RDO

Due to the MM digit structure, the MM strip channel identifier in the RDO's was set to a wrong value. This was not causing problems downstream because the channel data member of the RDO was set to the right value, but it's better to have consistent values.

modified: MuonSpectrometer/MuonCnv/MuonByteStreamCnvTest/src/MM_DigitToRDO.cxx