FmService: Fix loss of audio if we exit from main activity

* Only can recreate when FM Radio is switched off.

Recreation Steps:
1. Enter the FM Radio app and toggle FM radio on.
2. Press the toggle again to switch off FM radio.
3. Press the back button on your device to close activity.
4. Enjoy no sound until you reboot your device.

Change-Id: I6457760a9425c568f6f5ce912a40029bd9fb630c