PCI: apple: Change MSI handling to handle 4-cell AIC fwspec form

AIC2 changes the IRQ fwspec to add a cell. Always use the second-to-last
cell for the MSI handling, so it will work for both AIC1 and AIC2 devices.
Signed-off-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220309192123.152028-2-marcan@marcan.st

drivers/pci/controller/pcie-apple.c

@@ -219,7 +219,7 @@ static int apple_msi_domain_alloc(struct irq_domain *domain, unsigned int virq,
 	if (hwirq < 0)
 		return -ENOSPC;
 
-	fwspec.param[1] += hwirq;
+	fwspec.param[fwspec.param_count - 2] += hwirq;
 
 	ret = irq_domain_alloc_irqs_parent(domain, virq, nr_irqs, &fwspec);
 	if (ret)