stats: have_value is a bool, not int

Change-Id: Id92c63f4e54ec1bf3411205be1bd268e1d184b03
diff --git a/src/stats.c b/src/stats.c
index 91cf839..411ecff 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -709,7 +709,7 @@
 {
 	struct osmo_stats_reporter *srep;
 	int32_t value;
-	int have_value;
+	bool have_value;
 
 	have_value = osmo_stat_item_get_next(item, &item->stats_next_id, &value) > 0;
 	if (!have_value) {