irqchip/MSI: Use irq_domain_update_bus_token instead of an open coded access

Now that we have irq_domain_update_bus_token(), switch everyone over
to it. The debugfs code thanks you for your continued support.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/drivers/irqchip/irq-mips-cpu.c b/drivers/irqchip/irq-mips-cpu.c
index b247f3c..0a8ed1c 100644
--- a/drivers/irqchip/irq-mips-cpu.c
+++ b/drivers/irqchip/irq-mips-cpu.c
@@ -240,7 +240,7 @@ static void mips_cpu_register_ipi_domain(struct device_node *of_node)
 					      ipi_domain_state);
 	if (!ipi_domain)
 		panic("Failed to add MIPS CPU IPI domain");
-	ipi_domain->bus_token = DOMAIN_BUS_IPI;
+	irq_domain_update_bus_token(ipi_domain, DOMAIN_BUS_IPI);
 }
 
 #else /* !CONFIG_GENERIC_IRQ_IPI */