Apply suggestions from code review

Co-authored-by: Masaki <mkozuki@nvidia.com>

Author: 2 people

torchao/prototype/custom_fp_utils.py

@@ -13,7 +13,7 @@
 #      - Values outside the representable range of Floatx after rounding are clamped to the maximum Floatx
 #      magnitude (sign is preserved).
 
-from enum import Enum
+from enum import Enum, auto
 
 import torch
 from torch import Tensor