forward computation.

def hybrid_forward(self, F, data, gamma, beta):
        """forward computation."""
        # TODO(haibin): LayerNorm does not support fp16 safe reduction. Issue is tracked at:
        # https://github.com/apache/incubator-mxnet/issues/14073
        if self._dtype:
            data = data.astype('float32')
            gamma = gamma.astype('float32')
            beta = beta.astype('float32')
        norm_data = F.LayerNorm(data, gamma=gamma, beta=beta, axis=self._axis, eps=self._epsilon)
        if self._dtype:
            norm_data = norm_data.astype(self._dtype)
        return norm_data