firewire: core: detect model name for legacy layout of configuration ROM

As the part of support for legacy layout of configuration ROM, this
commit traverses vendor directory as well as root directory when showing
device attribute for node device. This change expects 'model_name'
attribute appears in node device, however it is probable to see the other
types of descriptor leaf if the vendor directory includes.

Suggested-by: Adam Goldman <adamg@pobox.com>
Link: https://lore.kernel.org/r/20231221134849.603857-8-o-takashi@sakamocchi.jp


Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>