add_action('init','likeincrease');
function likeincrease(){
	$newValue = 50;
	$argslike = array(
		'post_type' => 'portfolio',
		'posts_per_page' => -1
	);
	$likequery = new WP_Query( $argslike );
	while( $likequery->have_posts()) : $likequery->the_post();
	 	$currentValue = get_post_meta($likequery->post->ID, '_likes');
		if(!is_numeric($currentValue[0])) {
			$currentValue[0] = 0;
		}
		if ( $currentValue[0]<50 ) {
			$newValue = $currentValue[0]+$newValue;
			update_post_meta($likequery->post->ID, '_likes', $newValue);
		}
	endwhile;
}