fix call correct _field_for_schema function

Author: mvanderlee

marshmallow_dataclass/__init__.py

@@ -770,8 +770,8 @@ def _field_for_generic_type(
         if origin in (dict, Dict, collections.abc.Mapping, Mapping):
             dict_type = type_mapping.get(Dict, marshmallow.fields.Dict)
             return dict_type(
-                keys=field_for_schema(arguments[0], base_schema=base_schema),
-                values=field_for_schema(arguments[1], base_schema=base_schema),
+                keys=_field_for_schema(arguments[0], base_schema=base_schema),
+                values=_field_for_schema(arguments[1], base_schema=base_schema),
                 **metadata,
             )