lib: change var to let in stream_base_commons

PR-URL: #30426
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/internal/stream_base_commons.js

@@ -111,16 +111,15 @@ function createWriteWrap(handle) {
 function writevGeneric(self, data, cb) {
   const req = createWriteWrap(self[kHandle]);
   const allBuffers = data.allBuffers;
-  var chunks;
-  var i;
+  let chunks;
   if (allBuffers) {
     chunks = data;
-    for (i = 0; i < data.length; i++)
+    for (let i = 0; i < data.length; i++)
       data[i] = data[i].chunk;
   } else {
     chunks = new Array(data.length << 1);
-    for (i = 0; i < data.length; i++) {
-      var entry = data[i];
+    for (let i = 0; i < data.length; i++) {
+      const entry = data[i];
       chunks[i * 2] = entry.chunk;
       chunks[i * 2 + 1] = entry.encoding;
     }