mxf group reader: fix timecode object comparison
mxf group reader: fix timecode object comparison

Was wrongly comparing the pointer values

xunchangguo/BMX,Limecraft/ebu-bmx,Limecraft/ebu-bmx,kierank/bmxlib-bmx,stuarthicks/bmx,xunchangguo/BMX,xunchangguo/BMX,stuarthicks/bmx,kierank/bmxlib-bmx,stuarthicks/bmx,ebu/ebu-bmx,Limecraft/ebu-bmx,ebu/ebu-bmx,kierank/bmxlib-bmx,ebu/ebu-bmx