Initialize mask for tril/triu on correct device
Initialize mask for tril/triu on correct device

chainer/chainer,niboshi/chainer,niboshi/chainer,chainer/chainer,hvy/chainer,hvy/chainer,chainer/chainer,hvy/chainer,niboshi/chainer,pfnet/chainer,niboshi/chainer,hvy/chainer,chainer/chainer