HADOOP-15172. Fix the javadoc warning in WriteOperationHelper.java

Signed-off-by: Akira Ajisaka <aajisaka@apache.org>

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/WriteOperationHelper.java

@@ -82,6 +82,7 @@ public class WriteOperationHelper {
   /**
    * Constructor.
    * @param owner owner FS creating the helper
+   * @param conf Configuration object
    *
    */
   protected WriteOperationHelper(S3AFileSystem owner, Configuration conf) {