fix incorrect usage of tpl_getMediaFile

feed.php

@@ -53,7 +53,7 @@ $rss->cssStyleSheet  = DOKU_URL.'lib/exe/css.php?s=feed';
 
 $image        = new FeedImage();
 $image->title = $conf['title'];
-$image->url   = tpl_getMediaFile('favicon.ico', true);
+$image->url   = tpl_getMediaFile(array(':wiki:favicon.ico', ':favicon.ico', 'images/favicon.ico'), true);
 $image->link  = DOKU_URL;
 $rss->image   = $image;