wp-admin-logo.php

<?php
  add_action('login_enqueue_scripts', function() { ?>
		<style type="text/css">
			#login h1 a, .login h1 a {
				background-image: url(<?php echo get_stylesheet_directory_uri(); ?>/images/logo.png);
				width: 185px;
				height: 185px;
				background-size: initial;
			}
		</style>
	<?php });