Optimize depth2space function by reducing operations number
Optimize depth2space function by reducing operations number

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