hal: voice: fix no sound issue in voice call

- no audio heard in voice call scenario because in_call state
  is not updated when voice usecase is stopped. This results in
  not starting voice call usecase when setting up next call.

- fix is to set in_call state to false in voice_stop_usecase().
  This is to ensure that voice usecase is stopped and in_call
  state is update properly.

Bug: 29581781
Change-Id: Id27f2b90cf0de678b39d8efb712045f1ee7b2aaf