irqchip/mbigen: Don't clear eventid when freeing an MSI

mbigen_write_msg clears eventid bits of a mbigen register
when free a interrupt, because msi_domain_deactivate memset
struct msg to zero. Then multiple mbigen pins with zero eventid
will report the same interrupt number.

The eventid clear call trace:
                free_irq
                __free_irq
                irq_shutdown
                irq_domain_deactivate_irq
                __irq_domain_deactivate_irq
                __irq_domain_deactivate_irq
                msi_domain_deactivate
                platform_msi_write_msg
                mbigen_write_msg
Signed-off-by: Jianguo Chen <chenjianguo3@huawei.com>
[maz: massaged subject]
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

drivers/irqchip/irq-mbigen.c

@@ -161,6 +161,9 @@ static void mbigen_write_msg(struct msi_desc *desc, struct msi_msg *msg)
 	void __iomem *base = d->chip_data;
 	u32 val;
 
+	if (!msg->address_lo && !msg->address_hi)
+		return;
+ 
 	base += get_mbigen_vec_reg(d->hwirq);
 	val = readl_relaxed(base);