iommu/vt-d: Take CONFIG_PCI_ATS into account

pci_dev::physfn is only available when CONFIG_PCI_ATS is set. The recent
fix for the irqdomain rework missed that dependency which makes the build
fail when CONFIG_PCI_ATS=n.

Add the necessary #ifdeffery.
Reported-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Fixes: ff828729 ("iommu/vt-d: Cure VF irqdomain hickup")
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Joerg Roedel <joro@8bytes.org>

drivers/iommu/intel/dmar.c

@@ -335,7 +335,9 @@ static void  dmar_pci_bus_del_dev(struct dmar_pci_notify_info *info)
 
 static inline void vf_inherit_msi_domain(struct pci_dev *pdev)
 {
+#ifdef CONFIG_PCI_ATS
 	dev_set_msi_domain(&pdev->dev, dev_get_msi_domain(&pdev->physfn->dev));
+#endif
 }
 
 static int dmar_pci_bus_notifier(struct notifier_block *nb,