firewire: core: utilize kref to maintain fw_node with reference counting

Current implementation directly uses refcount_t to maintain the life time
of fw_node, while kref is available for the same purpose.

This commit replaces the implementation with kref.

Link: https://lore.kernel.org/r/20240801022629.31857-1-o-takashi@sakamocchi.jpSigned-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

drivers/firewire/core-topology.c

@@ -39,7 +39,7 @@ static struct fw_node *fw_node_create(u32 sid, int port_count, int color)
 	node->initiated_reset = phy_packet_self_id_zero_get_initiated_reset(sid);
 	node->port_count = port_count;
 
-	refcount_set(&node->ref_count, 1);
+	kref_init(&node->kref);
 	INIT_LIST_HEAD(&node->link);
 
 	return node;

drivers/firewire/core.h

@@ -183,7 +183,8 @@ struct fw_node {
 			 * local node to this node. */
 	u8 max_depth:4;	/* Maximum depth to any leaf node */
 	u8 max_hops:4;	/* Max hops in this sub tree */
-	refcount_t ref_count;
+
+	struct kref kref;
 
 	/* For serializing node topology into a list. */
 	struct list_head link;
@@ -196,15 +197,21 @@ struct fw_node {
 
 static inline struct fw_node *fw_node_get(struct fw_node *node)
 {
-	refcount_inc(&node->ref_count);
+	kref_get(&node->kref);
 
 	return node;
 }
 
+static void release_node(struct kref *kref)
+{
+	struct fw_node *node = container_of(kref, struct fw_node, kref);
+
+	kfree(node);
+}
+
 static inline void fw_node_put(struct fw_node *node)
 {
-	if (refcount_dec_and_test(&node->ref_count))
-		kfree(node);
+	kref_put(&node->kref, release_node);
 }
 
 void fw_core_handle_bus_reset(struct fw_card *card, int node_id,