Bluetooth: Controller: Deinit ticker

ticker_is_initialized() should only return true when the ticker is
running (triggered regularly). Users like nrf_flash_sync_is_required()
depend on this behavior.

When the bluetooth controller driver is closed, ll_deinit() calls
lll_deinit(), which stops the ticker from being triggered. Also
deinitialize the ticker to ensure that ticker_is_initialized() returns
false.

Signed-off-by: Marco Widmer <marco.widmer@bytesatwork.ch>