Fix comment on clearing padding.

Author: Japin Li
Discussion: https://www.postgresql.org/message-id/MEYP282MB16696317B5DA7D0D92306149B627A@MEYP282MB1669.AUSP282.PROD.OUTLOOK.COM

Author: hlinnaka

contrib/pg_stat_statements/pg_stat_statements.c

@@ -1257,7 +1257,7 @@ pgss_store(const char *query, uint64 queryId,
 
 	/* Set up key for hashtable search */
 
-	/* memset() is required when pgssHashKey is without padding only */
+	/* clear padding */
 	memset(&key, 0, sizeof(pgssHashKey));
 
 	key.userid = GetUserId();