don't increment num_batches_tracked if not tracking running stats

tinygrad/nn/__init__.py

@@ -39,7 +39,7 @@ class BatchNorm2d:
         self.running_mean.assign((1-self.momentum) * self.running_mean + self.momentum * batch_mean.detach())
         self.running_var.assign((1-self.momentum) * self.running_var +
                                 self.momentum * prod(y.shape[1:])/(prod(y.shape[1:])-y.shape[2]) * batch_var.detach())
-      self.num_batches_tracked += 1
+        self.num_batches_tracked += 1
     else:
       batch_mean = self.running_mean
       # NOTE: this can be precomputed for static inference. we expand it here so it fuses