Silence Wparentheses warning

`suggest parentheses around ‘&&’ within ‘||’` produced by gcc and clang.
Reproduced in gcc versions 4.8 - 7.3.
Reviewed-by: NHeikki Linnakangas <hlinnakangas@pivotal.io>
Reviewed-by: NMelanie Plageman <mplageman@pivotal.io>

src/backend/optimizer/plan/planner.c

@@ -638,10 +638,10 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	if (parse->setOperations)
 		flatten_simple_union_all(root);
 
-	if (parent_root && parent_root->is_correlated_subplan ||
-		(Gp_role == GP_ROLE_DISPATCH) &&
+	if ((parent_root && parent_root->is_correlated_subplan) ||
+		((Gp_role == GP_ROLE_DISPATCH) &&
 		root->config->is_under_subplan &&
-		IsSubqueryCorrelated(parse))
+		IsSubqueryCorrelated(parse)))
 	{
 		root->is_correlated_subplan = true;
 		/*