Keep the death recipient alive

Binder doesn't hold on to the death recipient.
This caused audio server to miss notifications about system server
death.

Fixes: 153080001
Test: Manual verification of killing the system process.
Change-Id: Iad1b2d4c5348d3d9917efc6838e86b736fa33094
diff --git a/services/audiopolicy/service/CaptureStateNotifier.h b/services/audiopolicy/service/CaptureStateNotifier.h
index 4ca6601..166de2a 100644
--- a/services/audiopolicy/service/CaptureStateNotifier.h
+++ b/services/audiopolicy/service/CaptureStateNotifier.h
@@ -17,6 +17,7 @@
 #pragma once
 
 #include <mutex>
+#include <binder/IBinder.h>
 #include <utils/StrongPointer.h>
 
 namespace android {
@@ -63,6 +64,7 @@
 private:
     std::mutex mMutex;
     sp<media::ICaptureStateListener> mListener;
+    sp<IBinder::DeathRecipient> mDeathRecipient;
     bool mActive;
 
     class DeathRecipient;