HDFS-16311. Metric metadataOperationRate calculation error in DataNodeVolumeMetrics (#3636)

Reviewed-by: Ayush Saxena <ayushsaxena@apache.org>
(cherry picked from commit 1c1cf64616f34d039cf9246da9613914aa870515)

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

@@ -284,6 +284,6 @@ public class DataNodeVolumeMetrics {
 
   public void addFileIoError(final long latency) {
     totalFileIoErrors.incr();
-    metadataOperationRate.add(latency);
+    fileIoErrorRate.add(latency);
   }
 }