[style] consistent nn. and nn.functional: part 4 examples (#12156)

* consistent nn. and nn.functional: p4 examples

* restore

examples/research_projects/deebert/src/modeling_highway_roberta.py

@@ -1,6 +1,6 @@
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-import torch.nn as nn
+from torch import nn
 from torch.nn import CrossEntropyLoss, MSELoss
 
 from transformers import RobertaConfig