Bug 1037880 - FM radio should stop sound in speaker mode when I receive ...

...an incoming call
We didn't reset |_previousFMRadioState| and |_previousEnablingState| here,  so I think there would be a problem with this case:

  - User opened FM radio app, FM radio is turned on
  - A call is coming, user picked up and hang up later
  - User turned off the FM radio, but leave the FM radio app opened
  - Another call is  coming, user picked up and hang up later

according to the codes, the FM radio will be turned on, right?