Give this a shot:
add_filter( 'generate_navigation_logo_output', 'tu_remove_nav_logo_link' );
function tu_remove_nav_logo_link( $output ) {
if ( ! function_exists( 'generate_menu_plus_get_defaults' ) ) {
return $output;
}
$settings = wp_parse_args(
get_option( 'generate_menu_plus_settings', array() ),
generate_menu_plus_get_defaults()
);
return sprintf(
'<div class="site-logo sticky-logo navigation-logo">
<img class="header-image" src="%1$s" alt="%2$s" />
</div>',
esc_url( apply_filters( 'generate_navigation_logo', $settings['sticky_menu_logo'] ) ),
esc_attr( apply_filters( 'generate_logo_title', get_bloginfo( 'name', 'display' ) ) )
);
}