hal: Avoid A2dp route updation for delayed a2dp/hfp disconnect

- Existing code routes to speaker until stream goes to
  standby on A2dp disconnect. This is done to not block
  writes from audioflinger.
- Consider a dual a2dp/hfp scenario with A2dp connected
  and hfp being constantly reconnected.
- In failure case, routing=0 from hfp disconnect comes in
  late i.e. during hfp reconnect. Stream is resumed and
  until hfp connect is processed, it is routed to speaker.
- Fix this by not routing to speaker if A2dp has not
  disconnected by checking lower stack.

Change-Id: Idd6c827a391777e943b3d59f33f8f4e98f98e802
diff --git a/hal/audio_hw.c b/hal/audio_hw.c
index 6097028..dca1602 100644
--- a/hal/audio_hw.c
+++ b/hal/audio_hw.c
@@ -3596,7 +3596,8 @@
          * Avoid this by routing audio to speaker until standby.
          */
         if ((out->devices & AUDIO_DEVICE_OUT_ALL_A2DP) &&
-                (val == AUDIO_DEVICE_NONE)) {
+                (val == AUDIO_DEVICE_NONE) &&
+                !audio_extn_a2dp_is_ready()) {
                 val = AUDIO_DEVICE_OUT_SPEAKER;
         }
         /* To avoid a2dp to sco overlapping / BT device improper state