fix stream option not working with to_gpu
fix stream option not working with to_gpu

hvy/chainer,delta2323/chainer,hvy/chainer,jnishi/chainer,tkerola/chainer,jnishi/chainer,ktnyt/chainer,keisuke-umezawa/chainer,jnishi/chainer,okuta/chainer,okuta/chainer,chainer/chainer,wkentaro/chainer,niboshi/chainer,niboshi/chainer,wkentaro/chainer,ktnyt/chainer,okuta/chainer,hvy/chainer,wkentaro/chainer,keisuke-umezawa/chainer,aonotas/chainer,ktnyt/chainer,ronekko/chainer,keisuke-umezawa/chainer,hvy/chainer,keisuke-umezawa/chainer,pfnet/chainer,jnishi/chainer,chainer/chainer,wkentaro/chainer,okuta/chainer,anaruse/chainer,rezoo/chainer,chainer/chainer,niboshi/chainer,chainer/chainer,ktnyt/chainer,niboshi/chainer,kashif/chainer