powerpc/pseries: Fix oops with MSIs when missing EEH PEs

The new EEH code introduced a small regression, if the EEH PEs
are missin (which happens currently in qemu for example), it
will deref a NULL pointer in the MSI code.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/pseries/msi.c

@@ -220,7 +220,8 @@ static struct device_node *find_pe_dn(struct pci_dev *dev, int *total)
 
 	/* Get the top level device in the PE */
 	edev = of_node_to_eeh_dev(dn);
-	edev = list_first_entry(&edev->pe->edevs, struct eeh_dev, list);
+	if (edev->pe)
+		edev = list_first_entry(&edev->pe->edevs, struct eeh_dev, list);
 	dn = eeh_dev_to_of_node(edev);
 	if (!dn)
 		return NULL;