[timer] Initialize i with zero

In case no timers were registered the result was not defined.
diff --git a/openbsc/src/timer.c b/openbsc/src/timer.c
index 6f974a2..ffeb4ab 100644
--- a/openbsc/src/timer.c
+++ b/openbsc/src/timer.c
@@ -176,7 +176,7 @@
 int bsc_timer_check(void)
 {
 	struct timer_list *timer;
-	int i;
+	int i = 0;
 
 	llist_for_each_entry(timer, &timer_list, entry) {
 		i++;