HDFS-16712. Fix incorrect placeholder in DataNode.java (#4672). Contributed by ZanderXu.

Signed-off-by: Ayush Saxena <ayushsaxena@apache.org>

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java

@@ -3529,7 +3529,7 @@ public class DataNode extends ReconfigurableBase
     try {
       return getDiskBalancer().queryWorkStatus().toJsonString();
     } catch (IOException ex) {
-      LOG.debug("Reading diskbalancer Status failed. ex:{}", ex);
+      LOG.debug("Reading diskbalancer Status failed.", ex);
       return "";
     }
   }