Add function doc for infer_batch_loss() function in model.py for DS2.
Add function doc for infer_batch_loss() function in model.py for DS2.

qingqing01/models,qingqing01/models,PaddlePaddle/models,qingqing01/models,kuke/models,Superjom/models-1,lcy-seso/models,Superjom/models-1,kuke/models,kuke/models,xinghai-sun/models,PaddlePaddle/models,kuke/models,Superjom/models-1,lcy-seso/models,xinghai-sun/models,lcy-seso/models,xinghai-sun/models,PaddlePaddle/models,xinghai-sun/models