const-ness error in ReqSubRecord<T>

Looking at other similar constructs, will eventually need similar fixes for
those as well.
Fix Compile errors: FNV:IMGSRecordAPI
Fix Compile errors: FNV:IMADRecordAPI
Fix Compile errors: FNV:HUNGRecordAPI
Fix Compile errors: FNV:FLSTRecordAPI
Fix Compile errors: FNV:ECZNRecordAPI
Fix Compile errors: FNV:DOBJRecordAPI
Fix Compile errors: FNV:DEHYRecordAPI
Fix Compile errors: FNV:CSNORecordAPI

Seems to be missing some fields though