audio: Fixed compiler warning

Added --unused tag to avoid compilation error

CRs-fixed: 1021714
Change-Id: I57fd9eb62d8548468cb10bf23498809867fbbc61
diff --git a/hal/audio_extn/pm.c b/hal/audio_extn/pm.c
index 7b76f60..f748dec 100644
--- a/hal/audio_extn/pm.c
+++ b/hal/audio_extn/pm.c
@@ -32,6 +32,7 @@
 
 #include "pm.h"
 #include <cutils/log.h>
+#include <cutils/str_parms.h>
 
 static s_audio_subsys audio_ss;
 
@@ -118,7 +119,7 @@
     }
 }
 
-void audio_extn_pm_event_notifier(void *client_data, enum pm_event event)
+void audio_extn_pm_event_notifier(void *client_data __unused, enum pm_event event)
 {
     pm_client_event_acknowledge(audio_ss.pm_handle, event);