Fix SQLAlchemy default sort order when column name is ambiguous.

Instead of sorting on the raw column name, sort on the attribute we found. This fixes sorting for column names that are ambiguous due to table joins.

flask_admin/contrib/sqla/view.py

@@ -716,7 +716,7 @@ class ModelView(BaseModelView):
 
             join_tables, attr = self._get_field_with_path(field)
 
-            return join_tables, field, direction
+            return join_tables, attr, direction
 
         return None