[Fix] fix copy&paste typo in BackendClient (#622)

Author: keytouch

flink-doris-connector/src/main/java/org/apache/doris/flink/backend/BackendClient.java

@@ -71,7 +71,7 @@ public BackendClient(Routing routing, DorisReadOptions readOptions) {
                         ? ConfigurationOptions.DORIS_REQUEST_RETRIES_DEFAULT
                         : readOptions.getRequestRetries();
         this.thriftMaxMessageSize =
-                readOptions.getRequestRetries() == null
+                readOptions.getThriftMaxMessageSize() == null
                         ? ConfigurationOptions.DORIS_THRIFT_MAX_MESSAGE_SIZE_DEFAULT
                         : readOptions.getThriftMaxMessageSize();
         logger.trace(