alsa_sound: select correct BT device pair for car-kit use case

- No audio during call when connected to Alpine NTG2.5 carkit
- BT-SCO Rx as the output device and Hanset Dual Mic as the
  input device is selected which is not a valid pair
- Select BT-SCO Tx as input when BT-SCO Rx is the output device

CRs-Fixed: 585953
Change-Id: I6a5220bf14fd2d7476196b9b1730c0646beec3a1