aaudio: rename timestamp variables

There were several different timestamp variables with slightly
different meaning but with the same name.
That made it hard to debug the code.

Test: atest CtsNativeMediaAAudioTestCases
Change-Id: Iebf438676925c698377abe02c81f3d559829318a
diff --git a/media/libaaudio/src/client/AudioStreamInternal.h b/media/libaaudio/src/client/AudioStreamInternal.h
index 3bb9e1e..1c88f52 100644
--- a/media/libaaudio/src/client/AudioStreamInternal.h
+++ b/media/libaaudio/src/client/AudioStreamInternal.h
@@ -163,7 +163,7 @@
 
     AAudioServiceInterface  &mServiceInterface;   // abstract interface to the service
 
-    SimpleDoubleBuffer<Timestamp>  mAtomicTimestamp;
+    SimpleDoubleBuffer<Timestamp>  mAtomicInternalTimestamp;
 
     AtomicRequestor          mNeedCatchUp;   // Ask read() or write() to sync on first timestamp.