Hi,
Moodle page header used to be a clickable area, and also a good place to add an image using some Custom CSS, but this was depreciated after lots of people became annoyed because every time they wanted to click a menu item in the navbar, which is above the page header area, they were clicking too soon and ended up being taken to the home page from wherever they where.
So, are you absolutely sure you want the banner to be click-able?
It's not a good idea really unless you want to direct people to another page or outside your Moodle site completely.
Cheers
Mary