Wordpress - How do I change the login logo URL and hover title?

Try these filters instead

// changing the logo link from wordpress.org to your site
function mb_login_url() {  return home_url(); }
add_filter( 'login_headerurl', 'mb_login_url' );

// changing the alt text on the logo to show your site name
function mb_login_title() { return get_option( 'blogname' ); }
add_filter( 'login_headertitle', 'mb_login_title' );

Though if you're on a Network/MultiSite you might need network_home_url() instead