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/AudioStreamInternalPlay.cpp b/media/libaaudio/src/client/AudioStreamInternalPlay.cpp
index 0884fca..6af8e7d 100644
--- a/media/libaaudio/src/client/AudioStreamInternalPlay.cpp
+++ b/media/libaaudio/src/client/AudioStreamInternalPlay.cpp
@@ -71,7 +71,7 @@
 
     mClockModel.stop(AudioClock::getNanoseconds());
     setState(AAUDIO_STREAM_STATE_PAUSING);
-    mAtomicTimestamp.clear();
+    mAtomicInternalTimestamp.clear();
     return mServiceInterface.pauseStream(mServiceStreamHandle);
 }