irqchip/renesas-irqc: Use platform_get_irq_optional() to get the interrupt

platform_get_resource(pdev, IORESOURCE_IRQ, ..) relies on static
allocation of IRQ resources in DT core code, this causes an issue
when using hierarchical interrupt domains using "interrupts" property
in the node as this bypassed the hierarchical setup and messed up the
irq chaining.

In preparation for removal of static setup of IRQ resource from DT core
code use platform_get_irq_optional().
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211216182121.5323-2-prabhakar.mahadev-lad.rj@bp.renesas.com

drivers/irqchip/irq-renesas-irqc.c

@@ -126,7 +126,6 @@ static int irqc_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	const char *name = dev_name(dev);
 	struct irqc_priv *p;
-	struct resource *irq;
 	int ret;
 	int k;
 
@@ -142,13 +141,15 @@ static int irqc_probe(struct platform_device *pdev)
 
 	/* allow any number of IRQs between 1 and IRQC_IRQ_MAX */
 	for (k = 0; k < IRQC_IRQ_MAX; k++) {
-		irq = platform_get_resource(pdev, IORESOURCE_IRQ, k);
-		if (!irq)
+		ret = platform_get_irq_optional(pdev, k);
+		if (ret == -ENXIO)
 			break;
+		if (ret < 0)
+			goto err_runtime_pm_disable;
 
 		p->irq[k].p = p;
 		p->irq[k].hw_irq = k;
-		p->irq[k].requested_irq = irq->start;
+		p->irq[k].requested_irq = ret;
 	}
 
 	p->number_of_irqs = k;