hal: Fix audio leak issue on speaker during A2DP and SCO concurrency.

-To ensure that A2DP stream is suspended before SCO starts, force
route to speaker is done, update the logic to ensure that force
routing to speaker only happens when there is no A2DP device active.
-Ensure that a2dp_start retry happens on routing request if the earlier
start failed.

Change-Id: I29ea0d8857fc4b9d837f9954423861be9b43b9a6