tools: ynl: fix undefined variable name

This variable used in the error path was not defined according to Ruff.
msg_format.attr_set is used instead, presumably the one that was
supposed to be used originally.

This is linked to Ruff error F821 [1]:

  An undefined name is likely to raise NameError at runtime.

Fixes: 1769e2b ("tools/net/ynl: Add 'sub-message' attribute decoding to ynl")
Link: https://docs.astral.sh/ruff/rules/undefined-name/ [1]
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Reviewed-by: Donald Hunter <[email protected]>
Reviewed-by: Asbjørn Sloth Tønnesen <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: matttbe

tools/net/ynl/pyynl/lib/ynl.py

@@ -746,7 +746,7 @@ def _decode_sub_msg(self, attr, attr_spec, search_attrs):
                 subdict = self._decode(NlAttrs(attr.raw, offset), msg_format.attr_set)
                 decoded.update(subdict)
             else:
-                raise Exception(f"Unknown attribute-set '{attr_space}' when decoding '{attr_spec.name}'")
+                raise Exception(f"Unknown attribute-set '{msg_format.attr_set}' when decoding '{attr_spec.name}'")
         return decoded
 
     def _decode(self, attrs, space, outer_attrs = None):