Use Ember.set to set controller in Route.setup

Under specific circumstances that I could not identify, the following error is raised after clicking on a link to a route:

    Error while processing route: [route-name] Assertion Failed: You must use Ember.set() to set the `controller` property (of [route]) to `[controller]`.

This change fixes the error.

In my case, the `link-to` points to the same route with a different model, but I'm not sure this has any influence.