benchmark: fix incorrect base64 input in byteLength benchmark

PR-URL: #60841Fixes: #60836
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Deokjin Kim <deokjin81.kim@gmail.com>

Author: semimikoh

benchmark/buffers/buffer-bytelength-string.js

@@ -22,7 +22,7 @@ const chars = {
 functiongetInput(type,repeat,encoding){
 constoriginal=(repeat===1) ? chars[type] : chars[type].repeat(repeat);
 if(encoding==='base64'){
-Buffer.from(original,'utf8').toString('base64');
+returnBuffer.from(original,'utf8').toString('base64');
 }
 returnoriginal;
 }