fix Large R accessor in jet calibration
I ran into the issue that this [accessor| https://acode-browser1.usatlas.bnl.gov/lxr/source/athena/Reconstruction/Jet/JetUncertainties/Root/FlavourUncertaintyComponent.cxx#0368] needs to be non-static in order to work with several jet calibrations that might need different truth labels. @khoo