util: simplify code

Simplify code by using return value of Object.defineProperty directly.

PR-URL: #25162
Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com>
Reviewed-By: Masashi Hirano <shisama07@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Author: kkty

Diff for: lib/internal/util.js

@@ -260,10 +260,9 @@ function promisify(original) {
     if (typeof fn !== 'function') {
       throw new ERR_INVALID_ARG_TYPE('util.promisify.custom', 'Function', fn);
     }
-    Object.defineProperty(fn, kCustomPromisifiedSymbol, {
+    return Object.defineProperty(fn, kCustomPromisifiedSymbol, {
       value: fn, enumerable: false, writable: false, configurable: true
     });
-    return fn;
   }
 
   // Names to create an object from in case the callback receives multiple