Try the following filters in your functions.php
//wordpress.org > your link
function wp_305258_login_url() {
return home_url();
}
add_filter( 'login_headerurl', 'wp_305258_login_url' );
//alt text to your site name
function wp_305258_login_title() {
return get_option( 'blogname' );
}
add_filter( 'login_headertitle', 'wp_305258_login_title' );