Fatal Error Message

Hello everyone, could I kindly ask for some help as a new WP user

I was looking for intstructions to install WP-PostRatings as the “loading…” button just hangs after rating submission.

Came across this answer:

http://forums.lesterchan.net/index.php/topic,3198.0.html

Thus I place the following coding in my functions.php

function get_site_url(){
$domain = $_SERVER[‘SERVER_NAME’];
$domain = str_replace(‘www.’, ”, $domain);
$site_url = ‘http://’ . $domain;
return $site_url;
}

After updating this, I can’t do anything =( Getting this error message:

Fatal error: Cannot redeclare get_site_url() (previously declared in /home/vaneats1/public_html/wp-includes/link-template.php:1909) in /home/vaneats1/public_html/wp-content/themes/eco/functions.php on line 23

Totally bummed out, could anyone provide me with some advice? Thank you for your time and consideration!