"fix frigled test gradient of rnn" (#7166)
"fix frigled test gradient of rnn" (#7166)

* "fix frigled test gradient of rnn"

* "fix based on comments"

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