Docs: Add missing parameter documentation to the DocBlock for the deprecated `debug_fwrite()`.

See #32246.


git-svn-id: https://develop.svn.wordpress.org/trunk@36756 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/deprecated.php

@@ -2837,6 +2837,9 @@ function debug_fopen( $filename, $mode ) {
  * @see error_log()
  *
  * @link http://www.php.net/manual/en/function.error-log.php
+ *
+ * @param mixed  $fp     Unused.
+ * @param string $string Message to log.
  */
 function debug_fwrite( $fp, $string ) {
 	_deprecated_function( __FUNCTION__, 'error_log()' );