TrigEgammaHypo: Fix crash in AsgElectronLikelihoodTool.

When we create a standalone Egamma object here, we need to set the `author'
xAOD variable.  Otherwise, AsgElectronLikelihoodTool::accept will throw
an exception due to the missing xAOD variable.

This affects AthenaTrigRDO_MC_pp_v6 in TriggerTest.