fix Variable 'readDNMaxAttempts' to be private

Author: xiezhineng

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/StripeReader.java

@@ -119,7 +119,7 @@ void skip() {
   protected final RawErasureDecoder decoder;
   protected final DFSStripedInputStream dfsStripedInputStream;
   private long readTo = -1;
-  protected final int readDNMaxAttempts;
+  private final int readDNMaxAttempts;
 
   protected ECChunk[] decodeInputs;