firewire: core: fix to update generation field in topology map

The generation field of topology map is updated after initialized by zero.
The updated value of generation field is always zero, and is against
specification.

This commit fixes the bug.

Fixes: 7d138cb269db ("firewire: core: use spin lock specific to topology map")
Link: https://lore.kernel.org/r/20251114144421.415278-1-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

drivers/firewire/core-topology.c

diff --git a/drivers/firewire/core-topology.c b/drivers/firewire/core-topology.c
index 2f73bcd..ed3ae8c 100644
--- a/drivers/firewire/core-topology.c
+++ b/drivers/firewire/core-topology.c
@@ -441,12 +441,13 @@ static void update_topology_map(__be32 *buffer, size_t buffer_size, int root_nod
 				const u32 *self_ids, int self_id_count)
 {
 	__be32 *map = buffer;
+	u32 next_generation = be32_to_cpu(buffer[1]) + 1;
 	int node_count = (root_node_id & 0x3f) + 1;
 
 	memset(map, 0, buffer_size);
 
 	*map++ = cpu_to_be32((self_id_count + 2) << 16);
-	*map++ = cpu_to_be32(be32_to_cpu(buffer[1]) + 1);
+	*map++ = cpu_to_be32(next_generation);
 	*map++ = cpu_to_be32((node_count << 16) | self_id_count);
 
 	while (self_id_count--)