powerpc/pseries: Check for MSI-X also in rtas_msi_pci_irq_fixup()

We also need to check that the device isn't using MSI-X in the irq fixup
routine, otherwise we might leave MSI-Xs configured at boot.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>