hal: Use derived playback snd device during re-routing

- Playback is heard on both usb headset and speaker once
ringtone is stopped.
- Playback is routed to usb headset and speaker while ringtone
is active. This is because all active usecases are routed to
snd device that will be used by new usecase.
- Re-route existing usecases to derived snd device for playback
instead of routing all usecases to same device.

Change-Id: I8ef192dfa1796acb68a7a7774bfd98b1842a475c