doc: fix typo in buffer.md

'uint16arr' -> 'uint16array'

PR-URL: nodejs#38323
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

doc/api/buffer.md

@@ -205,7 +205,7 @@ console.log(uint32array);
 
 ```js
 const buf = Buffer.from('hello', 'utf16le');
-const uint16arr = new Uint16Array(
+const uint16array = new Uint16Array(
   buf.buffer,
   buf.byteOffset,
   buf.length / Uint16Array.BYTES_PER_ELEMENT);