Fix gram.y comment to match reality

There are other comments in there that don't precisely match what's
implemented, but this one confused me enough to be worth fixing.

Author: alvherre

src/backend/parser/gram.y

@@ -4545,10 +4545,10 @@ AlterUserMappingStmt: ALTER USER MAPPING FOR auth_ident SERVER name alter_generi
 /*****************************************************************************
  *
  *		QUERIES:
- *				CREATE POLICY name ON table FOR cmd TO role USING (qual)
- *					WITH CHECK (with_check)
- *				ALTER POLICY name ON table FOR cmd TO role USING (qual)
- *					WITH CHECK (with_check)
+ *				CREATE POLICY name ON table [FOR cmd] [TO role, ...]
+ *					[USING (qual)] [WITH CHECK (with_check)]
+ *				ALTER POLICY name ON table [TO role, ...]
+ *					[USING (qual)] [WITH CHECK (with_check)]
  *				DROP POLICY name ON table
  *
  *****************************************************************************/