[Non-VISHack][dtt2hdf] Transfer functions stored in reference have inverted phase

[terrencetec]

For some reason, when a saved transfer function references in a diaggui XML file read by dtt2hdf, the phase is inverted. Not sure if this is a bug in dtt2hdf or diaggui itself. This is observed on multiple occasions. I hope this is consistent. In this case, we can just invert the phase when reading transfer function references by VISHack. For now, we will assume that this is consistent and just invert the phase when reading transfer function references.