How can I redirect on a url after successful registration?

You used in_array wrong. There might be some redundancy in your function too(depending on what you’re doing). You could use something like this to redirect your users:

add_filter('login_redirect', 'redirect_previous_page', 10);

function redirect_previous_page(){
    global $user;
    if ( in_array( 'administrator', $user->roles ) ) {
        return admin_url();
    } else {
        return 'http://localhost/'; //add your link here
    } 
}