pd: fix typo in deepmd-kit-tmp/deepmd/pd/utils/dataloader.py (#4512)

Fix a typo introduced in #4479, which will cause an error if torch is
not installed.

![image](https://github.com/user-attachments/assets/3f9b0955-ec2b-46ac-9efa-1ed4b4e023eb)

cc @njzjz 

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Chores**
- Updated the import path for the `mix_entropy` function to reflect a
reorganization of utility functions.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Chun Cai <[email protected]>

deepmd/pd/utils/dataloader.py

@@ -36,7 +36,7 @@
 from deepmd.pd.utils.dataset import (
     DeepmdDataSetForLoader,
 )
-from deepmd.pt.utils.utils import (
+from deepmd.pd.utils.utils import (
     mix_entropy,
 )
 from deepmd.utils import random as dp_random