WordPress: Change Admin Favicon

general.php

add_action( 'admin_head', 'we_admin_favicon' );
/**
 * Change Admin Favicon
 *
 */
function we_admin_favicon() {
    if ( file_exists( CHILD_DIR . '/images/favicon.ico' ) )
        $favicon = CHILD_URL . '/images/favicon.ico';
    elseif ( file_exists( CHILD_DIR . '/images/favicon.gif' ) )
        $favicon = CHILD_URL . '/images/favicon.gif';
    elseif ( file_exists( CHILD_DIR . '/images/favicon.png' ) )
        $favicon = CHILD_URL . '/images/favicon.png';
    elseif ( file_exists( CHILD_DIR . '/images/favicon.jpg' ) )
        $favicon = CHILD_URL . '/images/favicon.jpg';
    else
        $favicon = PARENT_URL . '/images/favicon.ico';

    $favicon = apply_filters( 'genesis_favicon_url', $favicon );

    if ( $favicon )
    echo '<link rel="Shortcut Icon" href="' . esc_url( $favicon ) . '" type="image/x-icon" />' . "\n";
}