Minor fix on dtype cast
Minor fix on dtype cast

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