hal: fix no sound issue in voice call

No audio is observed in voice call scenario since in_call state
is not update when voice usecase is stopped. This results in not
starting voice call usecase when setting up next call.

Fix by setting in_call state as false in voice_stop_usecase(). This
is to ensure that voice usecase is stopped and in_call state is update
properly.

CRs-Fixed: 996510
Change-Id: I480bb14899d678a47df8a61fbdd208b75ef7b395
diff --git a/hal/voice.c b/hal/voice.c
index bff69a1..5fef205 100644
--- a/hal/voice.c
+++ b/hal/voice.c
@@ -132,6 +132,9 @@
 
     session->state.current = CALL_INACTIVE;
 
+    if (!voice_is_call_state_active(adev))
+        adev->voice.in_call = false;
+
     /* Disable sidetone only when no calls are active */
     if (!voice_is_call_state_active(adev))
         voice_set_sidetone(adev, uc_info->out_snd_device, false);