irqchip/loongson-pch-msi: Use irq_domain_create_hierarchy()

Use the irq_domain_create_hierarchy() helper to create the hierarchical
domain, which both serves as documentation and avoids poking at
irqdomain internals.
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Hsin-Yi Wang <hsinyi@chromium.org>
Tested-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230213104302.17307-19-johan+linaro@kernel.org

drivers/irqchip/irq-loongson-pch-msi.c

@@ -163,8 +163,8 @@ static int pch_msi_init_domains(struct pch_msi_data *priv,
 {
 	struct irq_domain *middle_domain, *msi_domain;
 
-	middle_domain = irq_domain_create_linear(domain_handle,
-						priv->num_irqs,
+	middle_domain = irq_domain_create_hierarchy(parent, 0, priv->num_irqs,
+						    domain_handle,
 						    &pch_msi_middle_domain_ops,
 						    priv);
 	if (!middle_domain) {
@@ -172,7 +172,6 @@ static int pch_msi_init_domains(struct pch_msi_data *priv,
 		return -ENOMEM;
 	}
 
-	middle_domain->parent = parent;
 	irq_domain_update_bus_token(middle_domain, DOMAIN_BUS_NEXUS);
 
 	msi_domain = pci_msi_create_irq_domain(domain_handle,