fix: fix a typo in #702 (#710)

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## Summary by CodeRabbit

- **Improvements**
- Enhanced the flexibility of data handling by modifying how data types
are processed, allowing for better adaptability based on context.

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Signed-off-by: Jinzhe Zeng <jinzhe.zeng@rutgers.edu>

dpdata/deepmd/comp.py

@@ -180,7 +180,7 @@ def dump(folder, data, set_size=5000, comp_prec=np.float32, remove_sets=True):
         dtypes = dpdata.system.LabeledSystem.DTYPES
     else:
         dtypes = dpdata.system.System.DTYPES
-    for dtype in dpdata.system.LabeledSystem.DTYPES:
+    for dtype in dtypes:
         if dtype.name in (
             "atom_numbs",
             "atom_names",