Release ICloseHandle instance after announcement listener is unregistered

Bug: b/170770415
Test: Presubmit
Change-Id: I3974fa2fd38717882758321c8abea98c993f990c
diff --git a/services/core/java/com/android/server/broadcastradio/hal2/RadioModule.java b/services/core/java/com/android/server/broadcastradio/hal2/RadioModule.java
index a0eafb4..b7e188c 100644
--- a/services/core/java/com/android/server/broadcastradio/hal2/RadioModule.java
+++ b/services/core/java/com/android/server/broadcastradio/hal2/RadioModule.java
@@ -392,6 +392,7 @@
                 } catch (RemoteException ex) {
                     Slog.e(TAG, "Failed closing announcement listener", ex);
                 }
+                hwCloseHandle.value = null;
             }
         };
     }