Use `if constexpr` instead of SFINAE to handle return values of type `void`. Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>