[SPARK-14554][SQL][FOLLOW-UP] use checkDataset to check the result

## What changes were proposed in this pull request?

address this comment: https://github.com/apache/spark/pull/12322#discussion_r59417359

## How was this patch tested?

N/A

Author: Wenchen Fan <wenchen@databricks.com>

Closes #12346 from cloud-fan/tmp.