icmap: make sure variable is initialized

shut up gcc warning

Reviewed-by: Steven Dake <sdake@redhat.com>
Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

exec/icmap.c

@@ -229,7 +229,7 @@ static int icmap_check_key_name(const char *key_name)
 
 static size_t icmap_get_valuetype_len(icmap_value_types_t type)
 {
-	size_t res;
+	size_t res = 0;
 
 	switch (type) {
 	case ICMAP_VALUETYPE_INT8: res = sizeof(int8_t); break;