hal: enable more default logs

Enable minimal default logging to know audio routes and sound
devices being enabled or disabled.

Change-Id: Ia5c67a654fc2f36bcb7cf722706a573b9e6c0a04
diff --git a/hal/msm8974/platform.c b/hal/msm8974/platform.c
index 01ab7bb..0d462a1 100644
--- a/hal/msm8974/platform.c
+++ b/hal/msm8974/platform.c
@@ -794,7 +794,7 @@
     if (snd_device >= SND_DEVICE_MIN && snd_device < SND_DEVICE_MAX)
         return device_table[snd_device];
     else
-        return "";
+        return "none";
 }
 
 void platform_add_backend_name(void *platform, char *mixer_path,