How to list categories in reverse alphabetical order?

Redefine arguments for ‘category’ taxonomy ONLY:

add_filter( 'get_terms_args', 'my_term_args', 10, 2 );

function my_term_args( $args, $taxonomies ) {
    // don't affect admin area passing back default arguments
    if ( is_admin() ) {
        return $args;
    }

    // check the taxonomy in use and redefine it's default arguments
    if( in_array( 'category', $taxonomies ) ) {
        $args['orderby']    = 'name';
        $args['order']      = 'DESC';
        $args['hide_empty'] = false;
    }

    return $args;
}

Also, get_terms() syntax you’ve posted is obsolete since version 4.5. The new syntax look like this:

<?php
$categories = get_terms( array(
    'taxonomy'   => 'category'
    'orderby'    => 'name',
    'order'      => 'DESC',
    'hide_empty' => false
) );