powerpc/pci: Fix broken INTx configuration via OF

powerpc/pci: Fix broken INTx configuration via OF

a9e1dbafbbe8 ("powerpc/pci: Use of_irq_parse_and_map_pci() helper")
replaced of_irq_parse_pci() + irq_create_of_mapping() with
of_irq_parse_and_map_pci(), but neglected to capture the virq
returned by irq_create_of_mapping(), so virq remained zero, which
caused INTx configuration to fail.

Save the virq value returned by of_irq_parse_and_map_pci() and correct
the virq declaration to match the of_irq_parse_and_map_pci() signature.

Fixes: a9e1dbafbbe8 "powerpc/pci: Use of_irq_parse_and_map_pci() helper"
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[bhelgaas: changelog]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>