Fix build due to merge of 7595842 and renaming due to 8eb87f0

I.e. rename mVideoCallback -> mCallback. Line with original name
was added in mwd, renaming was done in master. The renaming CL
was cherry-picked to mwd (and build probably fixed there).

Change-Id: I462a0fedd00293a148404e1419740bf492ae5de9
diff --git a/telecomm/java/android/telecom/VideoCallImpl.java b/telecomm/java/android/telecom/VideoCallImpl.java
index ba064cf..d1474fa 100644
--- a/telecomm/java/android/telecom/VideoCallImpl.java
+++ b/telecomm/java/android/telecom/VideoCallImpl.java
@@ -176,7 +176,7 @@
 
     /** {@inheritDoc} */
     public void removeVideoCallListener() {
-        mVideoCallListener = null;
+        mCallback = null;
         try {
             mVideoProvider.removeVideoCallback(mBinder);
         } catch (RemoteException e) {