utils: add missing header

The build breaks because convert_ts is missing.

Also utils.c depends on json_object_add_value_string, thus define one
when we don't use json-c.

Signed-off-by: Daniel Wagner <dwagner@suse.de>

Author: igaw

util/json.h

@@ -56,6 +56,8 @@ uint64_t util_json_object_get_uint64(struct json_object *obj);
 
 struct json_object;
 
+#define json_object_add_value_string(o, k, v)
+
 #endif
 
 #endif

util/utils.c

@@ -8,6 +8,8 @@
  */
 
 #include "utils.h"
+#include "types.h"
+#include "json.h"
 
 int hex_to_int(char c)
 {