Fixes sound panel create multiple SoundSettings activity

- Use FLAG_ACTIVITY_NEW_TASK to prevent activity stack contains
many activites

Fixes: 142231489
Test: 1. Press volume button and click in volume settings button
      2. Press Media Volume to open SoundSettings
      3. Repeat 1, Press Call Volume to open SoundSettings
      4. Repeat 1, Press Alarm Volume to open SoundSettings
      5. Press back, should see volume panel
Change-Id: I87cd75fbd43f77446191ad50ed7a002a2202337f