vat: fix static analysis warning

replace hand crafted version with existing vector function

Type: fix

Signed-off-by: Andreas Schultz <andreas.schultz@travelping.com>
Change-Id: I94834852469ed316c7bdbd48bb7f479648b2c8e5

src/vat/json_format.h

@@ -94,8 +94,7 @@ vat_json_set_string_copy (vat_json_node_t * json, const u8 * str)
 {
   u8 *ns = NULL;
   int len = strlen ((const char *) str);
-  vec_validate (ns, len);
-  memcpy ((char *) ns, (const char *) str, len + 1);
+  vec_validate_init_c_string (ns, str, len);
   vat_json_set_string (json, ns);
 }