Fixed a compilation error with passing in a MString reference.
Fixed a compilation error with passing in a MString reference.

sideeffects/HoudiniEngineForMaya,sonictk/HoudiniEngineForMaya,pokyfudywise/HoudiniEngineForMaya,pokyfudywise/HoudiniEngineForMaya,pokyfudywise/HoudiniEngineForMaya,sonictk/HoudiniEngineForMaya,sonictk/HoudiniEngineForMaya,sideeffects/HoudiniEngineForMaya,sideeffects/HoudiniEngineForMaya