cosmetic: explicitly init ho_ref start value

The static ho_ref seems to be implicitly initialized to zero, but let's make it
explicit for code readability.

Change-Id: I00493bcb7ef3e38fb8e0077c60c5bac7199f1073
diff --git a/src/libbsc/handover_logic.c b/src/libbsc/handover_logic.c
index ee7b683..4b86de7 100644
--- a/src/libbsc/handover_logic.c
+++ b/src/libbsc/handover_logic.c
@@ -93,7 +93,7 @@
 {
 	struct gsm_lchan *new_lchan;
 	struct bsc_handover *ho;
-	static uint8_t ho_ref;
+	static uint8_t ho_ref = 0;
 	int rc;
 
 	/* don't attempt multiple handovers for the same lchan at