fix stylesheet for banner and carousel module

[dirsen]

I find there is a bit of a problem in the default modules like banner and carousel, on the controller module is supposed to be added $this->document->addStyle('catalog/view/javascript/jquery/flexslider/flexslider.css'); before $this->document->addScript('catalog/view/javascript/jquery/flexslider/jquery.flexslider-min.js');
like in slideshow.php module controller.