Fix android_media_AudioSystem_getMasterMute return type.

Caused FPU stack overflow on x86.

Bug: 18023418
Change-Id: I0b8102cad5f5a883f615fa5dfa3017f56258a192
diff --git a/core/jni/android_media_AudioSystem.cpp b/core/jni/android_media_AudioSystem.cpp
index 33bb90bc..f099289 100644
--- a/core/jni/android_media_AudioSystem.cpp
+++ b/core/jni/android_media_AudioSystem.cpp
@@ -390,7 +390,7 @@
     return (jint) check_AudioSystem_Command(AudioSystem::setMasterMute(mute));
 }
 
-static jfloat
+static jboolean
 android_media_AudioSystem_getMasterMute(JNIEnv *env, jobject thiz)
 {
     bool mute;