Fix warnings in sgd_op.h
Fix warnings in sgd_op.h

reyoung/Paddle,Canpio/Paddle,jacquesqiao/Paddle,baidu/Paddle,baidu/Paddle,luotao1/Paddle,lcy-seso/Paddle,lcy-seso/Paddle,Canpio/Paddle,QiJune/Paddle,putcn/Paddle,jacquesqiao/Paddle,pkuyym/Paddle,pkuyym/Paddle,reyoung/Paddle,reyoung/Paddle,chengduoZH/Paddle,putcn/Paddle,lcy-seso/Paddle,tensor-tang/Paddle,pkuyym/Paddle,lcy-seso/Paddle,lcy-seso/Paddle,QiJune/Paddle,jacquesqiao/Paddle,chengduoZH/Paddle,Canpio/Paddle,jacquesqiao/Paddle,baidu/Paddle,PaddlePaddle/Paddle,QiJune/Paddle,QiJune/Paddle,PaddlePaddle/Paddle,Canpio/Paddle,chengduoZH/Paddle,tensor-tang/Paddle,tensor-tang/Paddle,tensor-tang/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,chengduoZH/Paddle,luotao1/Paddle,luotao1/Paddle,reyoung/Paddle,chengduoZH/Paddle,baidu/Paddle,putcn/Paddle,Canpio/Paddle,QiJune/Paddle,jacquesqiao/Paddle,PaddlePaddle/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,putcn/Paddle,PaddlePaddle/Paddle,pkuyym/Paddle,luotao1/Paddle,putcn/Paddle,baidu/Paddle,QiJune/Paddle,luotao1/Paddle,tensor-tang/Paddle,reyoung/Paddle,luotao1/Paddle,putcn/Paddle,pkuyym/Paddle,Canpio/Paddle,jacquesqiao/Paddle,Canpio/Paddle,Canpio/Paddle,pkuyym/Paddle,lcy-seso/Paddle,PaddlePaddle/Paddle