Fix possible race condition in Sensor CTS framework.

Change-Id: I68bf76add3e65315362be044f15374d9a02ce38a
diff --git a/tests/tests/hardware/src/android/hardware/cts/helpers/TestSensorEventListener.java b/tests/tests/hardware/src/android/hardware/cts/helpers/TestSensorEventListener.java
index 9b3a5e4..6567be2 100644
--- a/tests/tests/hardware/src/android/hardware/cts/helpers/TestSensorEventListener.java
+++ b/tests/tests/hardware/src/android/hardware/cts/helpers/TestSensorEventListener.java
@@ -118,7 +118,7 @@
     @Override
     public void onFlushCompleted(Sensor sensor) {
         CountDownLatch latch = mFlushLatch;
-        mFlushLatch = new CountDownLatch(1);
+        mFlushLatch = null;
         if(latch != null) {
             latch.countDown();
         }