genirq/msi: Initialize msi_alloc_info before calling msi_domain_prepare_irqs()

Since commit 5fe71d27 ("irqchip/gic-v3-its: Tag ITS device as shared if
allocating for a proxy device"), some of the devices are wrongly marked as
"shared" by the ITS driver on systems equipped with the ITS(es). The
problem is that the @info->flags may not be initialized anywhere and we end
up looking at random bits on the stack. That's obviously not good.

We can perform the initialization in the IRQ core layer before calling
msi_domain_prepare_irqs(), which is neat enough.

Fixes: 5fe71d27 ("irqchip/gic-v3-its: Tag ITS device as shared if allocating for a proxy device")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201218060039.1770-1-yuzenghui@huawei.com

kernel/irq/msi.c

@@ -402,7 +402,7 @@ int __msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
 	struct msi_domain_ops *ops = info->ops;
 	struct irq_data *irq_data;
 	struct msi_desc *desc;
-	msi_alloc_info_t arg;
+	msi_alloc_info_t arg = { };
 	int i, ret, virq;
 	bool can_reserve;