fix doc problems

mindspore/nn/layer/normalization.py

@@ -166,6 +166,8 @@ class _BatchNorm(Cell):
     def extend_repr(self):
         return 'num_features={}, eps={}, momentum={}, gamma={}, beta={}, moving_mean={}, moving_variance={}'.format(
             self.num_features, self.eps, self.momentum, self.gamma, self.beta, self.moving_mean, self.moving_variance)
+
+@constexpr
 def _channel_check(channel, num_channel):
     if channel != num_channel:
         raise ValueError("the input channel is not equal with num_channels")