Используйте, “преобразовывают в автоматическое свойство” на нескольких свойствах сразу

        // Change [110]FILES to new vars and loop them
        foreach([110]FILES['files'] as $key=>$val)
        {
            $i = 1;
            foreach($val as $v)
            {
                $field_name = "file_".$i;
                [110]FILES[$field_name][$key] = $v;
                $i++;   
            }
        }
        // Unset the useless one ;)
        unset([110]FILES['files']);

        // Put each errors and upload data to an array
        $error = array();
        $success = array();

        // main action to upload each file
        foreach([110]FILES as $field_name => $file)
        {
            if ( ! $this->upload->do_upload($field_name))
            {
                echo ' failed ';
            }else{
                echo ' success ';
            }
        }