SystemUI: Fix issue with Bluetooth tile

* Currently: Pair a device
* Open BT tile details ("details"), device is shown
* Disable bt via the switchbar, close the details via the "done" button
* Reopen the details -> the list is empty, neither "empty" text nor
  actual devices are shown

After this patch: Reopening the details turns on bt which in turn makes
 devices visible again

Change-Id: I1a0a5ebdcaca50bc821b0180f2109d00091eaa1c