Fix pointless comparison warning
Fix pointless comparison warning

pfnet/chainer,chainer/chainer,hvy/chainer,hvy/chainer,niboshi/chainer,niboshi/chainer,niboshi/chainer,chainer/chainer,wkentaro/chainer,hvy/chainer,okuta/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,hvy/chainer,chainer/chainer,wkentaro/chainer,okuta/chainer,wkentaro/chainer,wkentaro/chainer,okuta/chainer,chainer/chainer,niboshi/chainer,okuta/chainer,keisuke-umezawa/chainer,tkerola/chainer