WordPress Genesis Search Form - Search Restrict to Posts Only

// * Alter the Genesis Search for so that we can change the destination page and our querystring parameter.
add_filter ( 'genesis_search_form', 'mc_search_form', 10, 4 );
function mc_search_form($form, $search_text, $button_text, $label)
{

	$button_text = '';
	
	$onfocus = " onfocus=\"if (this.value == '$search_text') {this.value = '';}\"";
	
	$onblur = " onblur=\"if (this.value == '') {this.value = '$search_text';}\"";
	
	$form = '<form method="get" class="searchform search-form" action="' . home_url () . '/search" >' . $label . '
<input type="text" value="' . esc_attr ( $search_text ) . '" name="q" class="s search-input"' . $onfocus . $onblur . ' />
<input type="submit" class="searchsubmit search-submit" value="' . esc_attr ( $button_text ) . '" />
</form>';
	
	return $form;
}