[SPARK-21111][TEST][2.2] Fix the test failure of describe.sql

## What changes were proposed in this pull request?
Test failed in `describe.sql`.

We need to fix the related bug introduced in (#17649) in the follow-up PR to master.

## How was this patch tested?
N/A

Author: gatorsmile <gatorsmile@gmail.com>

Closes #18316 from gatorsmile/fix.

sql/core/src/test/resources/sql-tests/results/describe.sql.out

@@ -127,6 +127,7 @@ Provider            	parquet
 Num Buckets         	2                   	                    
 Bucket Columns      	[`a`]               	                    
 Sort Columns        	[`b`]               	                    
+Comment             	table_comment       	                    
 Table Properties    	[e=3]               	                    
 Location [not included in comparison]sql/core/spark-warehouse/t	                    
 Storage Properties  	[a=1, b=2]          	                    
@@ -157,6 +158,7 @@ Provider            	parquet
 Num Buckets         	2                   	                    
 Bucket Columns      	[`a`]               	                    
 Sort Columns        	[`b`]               	                    
+Comment             	table_comment       	                    
 Table Properties    	[e=3]               	                    
 Location [not included in comparison]sql/core/spark-warehouse/t	                    
 Storage Properties  	[a=1, b=2]