Use audio_mode_t consistently

It was int or uint32_t.
Also make getMode() const.

Change-Id: Ibe45aadbf413b9158e4dd17f2b3bcc6355288d37
diff --git a/services/audioflinger/AudioPolicyService.cpp b/services/audioflinger/AudioPolicyService.cpp
index 3f86d58..6b59538 100644
--- a/services/audioflinger/AudioPolicyService.cpp
+++ b/services/audioflinger/AudioPolicyService.cpp
@@ -185,7 +185,7 @@
                                                       device_address);
 }
 
-status_t AudioPolicyService::setPhoneState(int state)
+status_t AudioPolicyService::setPhoneState(audio_mode_t state)
 {
     if (mpAudioPolicy == NULL) {
         return NO_INIT;