hal: Add check for default backend on RX path

Add additional check for default backend entry in a concurrent
usecase scenario. Without this check there will be a failure
in matching common backend in a usecase involving TTY HCO handset
and speaker-headset combo. This failure leads to audio loss during
TTY HCO usecase.

Change-Id: I5a708551de06781b7c0e56d9973460fe806bf241
CRs-Fixed: 1078299