firewire: core: annotate fw_destroy_nodes with must-hold-lock

The function, fw_destroy_nodes(), is used widely within firewire-core
module. It has a prerequisite condition that struct fw_card.lock must
be hold in advance.

This commit adds annotation for it.

Link: https://lore.kernel.org/r/20250915234747.915922-7-o-takashi@sakamocchi.jp


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