firewire: core: use macro expression for gap count mismatch

The gap_count field is assigned to zero when mismatch is detected. In such
case, the macro expression is preferable since it is easy to understand
the situation.

This commit applies the idea.

Link: https://lore.kernel.org/r/20250913105737.778038-2-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

drivers/firewire/core-card.c

@@ -425,7 +425,7 @@ static void bm_work(struct work_struct *work)
 	 */
 	card->bm_generation = generation;
 
-	if (card->gap_count == 0) {
+	if (card->gap_count == GAP_COUNT_MISMATCHED) {
 		/*
 		 * If self IDs have inconsistent gap counts, do a
 		 * bus reset ASAP. The config rom read might never

drivers/firewire/core-topology.c

@@ -241,7 +241,7 @@ static struct fw_node *build_tree(struct fw_card *card, const u32 *sid, int self
 		// If PHYs report different gap counts, set an invalid count which will force a gap
 		// count reconfiguration and a reset.
 		if (phy_packet_self_id_zero_get_gap_count(self_id_sequence[0]) != gap_count)
-			gap_count = 0;
+			gap_count = GAP_COUNT_MISMATCHED;
 
 		update_hop_count(node);
 

drivers/firewire/core.h

@@ -27,6 +27,9 @@ struct fw_packet;
 
 /* -card */
 
+// This is the arbitrary value we use to indicate a mismatched gap count.
+#define GAP_COUNT_MISMATCHED	0
+
 extern __printf(2, 3)
 void fw_err(const struct fw_card *card, const char *fmt, ...);
 extern __printf(2, 3)