firewire: fill_bus_reset_event needs lock protection

Callers of fill_bus_reset_event() have to take card->lock.  Otherwise
access to node data may oops if node removal is in progress.

A lockless alternative would be

-	event->local_node_id = card->local_node->node_id;
+	tmp = fw_node_get(card->local_node);
+	event->local_node_id = tmp->node_id;
+	fw_node_put(tmp);

and ditto with the other node pointers which fill_bus_reset_event()
accesses.  But I went the locked route because one of the two callers
already holds the lock.  As a bonus, we don't need the memory barrier
anymore because device->generation and device->node_id are written in
a card->lock protected section.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Kristian Høgsberg <krh@redhat.com>