fix docstring

Signed-off-by: Jinzhe Zeng <[email protected]>

deepmd/dpmodel/common.py

@@ -125,7 +125,7 @@ def cast_precision(func: Callable[..., Any]) -> Callable[..., Any]:
     """A decorator that casts and casts back the input
     and output tensor of a method.
 
-    The decorator should be used in a classmethod.
+    The decorator should be used on an instance method.
 
     The decorator will do the following thing:
     (1) It casts input arrays from the global precision
@@ -201,17 +201,17 @@ def safe_cast_array(
 
     Parameters
     ----------
-    input : tf.Tensor
-        Input tensor
+    input : np.ndarray or None
+        Input array
     from_precision : str
         Array data type that is casted from
     to_precision : str
         Array data type that casts to
 
     Returns
     -------
-    tf.Tensor
-        casted Tensor
+    np.ndarray or None
+        casted array
     """
     if array_api_compat.is_array_api_obj(input):
         xp = array_api_compat.array_namespace(input)