stream: simplify Writable.prototype.cork()

This commit removes an unnecessary intermediate variable.

PR-URL: #20697
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_stream_writable.js

@@ -299,9 +299,7 @@ Writable.prototype.write = function(chunk, encoding, cb) {
 };
 
 Writable.prototype.cork = function() {
-  var state = this._writableState;
-
-  state.corked++;
+  this._writableState.corked++;
 };
 
 Writable.prototype.uncork = function() {