PCI: rcar-host: Pass proper IRQ domain to generic_handle_domain_irq()

Starting with commit dd26c1a ("PCI: rcar-host: Switch to
msi_create_parent_irq_domain()"), the MSI parent IRQ domain is NULL because
the object of type struct irq_domain_info passed to:

msi_create_parent_irq_domain() ->
  irq_domain_instantiate()() ->
    __irq_domain_instantiate()

has no reference to the parent IRQ domain. Using msi->domain->parent as an
argument for generic_handle_domain_irq() leads to below error:

	"Unable to handle kernel NULL pointer dereference at virtual address"

This error was identified while switching the upcoming RZ/G3S PCIe host
controller driver to msi_create_parent_irq_domain() (which was using a
similar pattern to handle MSIs (see link section)), but it was not tested
on hardware using the pcie-rcar-host controller driver due to lack of
hardware.

Fixes: dd26c1a ("PCI: rcar-host: Switch to msi_create_parent_irq_domain()")
Signed-off-by: Claudiu Beznea <[email protected]>
[mani: reworded subject and description]
Signed-off-by: Manivannan Sadhasivam <[email protected]>
Reviewed-by: Nam Cao <[email protected]>
Link: https://lore.kernel.org/all/[email protected]
Link: https://patch.msgid.link/[email protected]

Author: claudiubeznea

drivers/pci/controller/pcie-rcar-host.c

@@ -584,7 +584,7 @@ static irqreturn_t rcar_pcie_msi_irq(int irq, void *data)
 		unsigned int index = find_first_bit(&reg, 32);
 		int ret;
 
-		ret = generic_handle_domain_irq(msi->domain->parent, index);
+		ret = generic_handle_domain_irq(msi->domain, index);
 		if (ret) {
 			/* Unknown MSI, just clear it */
 			dev_dbg(dev, "unexpected MSI\n");