Hi,
There is no easy way to do that.
It would require some complex coding in the file administrator/components/com_hikashop/classes/filter.php and that would mean adding one more MySQL query for each choice of each filter to get the count so if you have a lot of products / filters / choices it can significantly slow down the display of the page even if done properly, which would mean more complex coding to precalculate these values in a "cache" table.
That's basically why there is no option to activate to easily do that: hard to code, and potentially problematic.
It's on our todo list but we didn't get to work on that yet.