Revert "firewire: core: shrink critical section of fw_card spinlock in bm_work"

This reverts commit 58231037.

The bus manager work has the race condition against fw_destroy_nodes()
called by fw_core_remove_card(). The acquition of spin lock of fw_card
is left as is again.

Link: https://lore.kernel.org/r/20250924131823.262136-2-o-takashi@sakamocchi.jp


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