Reset a session callback variable when tune is failed

Change-Id: I7c0188d916047f8331c74ce7a29b0a5228583979
diff --git a/media/java/android/media/tv/TvView.java b/media/java/android/media/tv/TvView.java
index 7110db9..e51745e 100644
--- a/media/java/android/media/tv/TvView.java
+++ b/media/java/android/media/tv/TvView.java
@@ -858,6 +858,7 @@
                     mSession.setStreamVolume(mStreamVolume);
                 }
             } else {
+                mSessionCallback = null;
                 if (mListener != null) {
                     mListener.onConnectionFailed(mInputId);
                 }