powerpc/axon_msi: Validate msi irq via chip_data

Instead of checking for rogue msi numbers via the irq_map host field
set the chip_data to h.host_data (which is the msic struct pointer)
at map and compare it in get_irq.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/cell/axon_msi.c

@@ -113,7 +113,7 @@ static void axon_msi_cascade(unsigned int irq, struct irq_desc *desc)
 		pr_devel("axon_msi: woff %x roff %x msi %x\n",
 			  write_offset, msic->read_offset, msi);
 
-		if (msi < NR_IRQS && virq_to_host(msi) == msic->irq_host) {
+		if (msi < NR_IRQS && irq_get_chip_data(msi) == msic) {
 			generic_handle_irq(msi);
 			msic->fifo_virt[idx] = cpu_to_le32(0xffffffff);
 		} else {
@@ -320,6 +320,7 @@ static struct irq_chip msic_irq_chip = {
 static int msic_host_map(struct irq_host *h, unsigned int virq,
 			 irq_hw_number_t hw)
 {
+	irq_set_chip_data(virq, h->host_data);
 	irq_set_chip_and_handler(virq, &msic_irq_chip, handle_simple_irq);
 
 	return 0;