hal: Fix teardown during back to back pause/play of WFD session

- When an active WFD session is paused/played continuously from
  the WFDClient app, the session tears down after a few iterations
  if touch tones are enabled.
- The output device is switched back and forth between speaker and
  proxy when the session is paused and played continuously.
  When this happens, sometimes, there is no backend to write the
  low latency output which results in pcm_write getting blocked.
- Fix the issue by not routing the low latency output to speaker
  if the previous device is proxy.

CRs-Fixed: 630234
Change-Id: I6bbe82badd3d5ee857e920430304c3a45c5b44c7