HDFS-11352. Add missing entry in CHANGES.txt.

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -216,6 +216,9 @@ Release 2.7.4 - UNRELEASED
     HDFS-11290. TestFSNameSystemMBean should wait until JMX cache is cleared.
     (Eric Krogen via aajisaka)
 
+    HDFS-11352. Potential deadlock in NN when failing over.
+    (Eric Krogen via aajisaka)
+
 Release 2.7.3 - 2016-08-25
 
   INCOMPATIBLE CHANGES