iommu/vt-d: fix bug in matching PCI devices with DRHD/RMRR descriptors

Commit "59ce0515cdaf iommu/vt-d: Update DRHD/RMRR/ATSR device scope
caches when PCI hotplug happens" introduces a bug, which fails to
match PCI devices with DMAR device scope entries if PCI path array
in the entry has more than one level.

For example, it fails to handle
[1D2h 0466 1] Device Scope Entry Type : 01
[1D3h 0467 1] Entry Length : 0A
[1D4h 0468 2] Reserved : 0000
[1D6h 0470 1] Enumeration ID : 00
[1D7h 0471 1] PCI Bus Number : 00
[1D8h 0472 2] PCI Path : 1C,04
[1DAh 0474 2] PCI Path : 00,02

And cause DMA failure on HP DL980 as:
DMAR:[fault reason 02] Present bit in context entry is clear
dmar: DRHD: handling fault status reg 602
dmar: DMAR:[DMA Read] Request device [02:00.2] fault addr 7f61e000

Reported-and-tested-by: Davidlohr Bueso <[e-mail]>
Signed-off-by: Jiang Liu <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/iommu/dmar.c

···
 	info->seg = pci_domain_nr(dev->bus);
 	info->level = level;
 	if (event == BUS_NOTIFY_ADD_DEVICE) {
-		for (tmp = dev, level--; tmp; tmp = tmp->bus->self) {
+		for (tmp = dev; tmp; tmp = tmp->bus->self) {
+			level--;
 			info->path[level].device = PCI_SLOT(tmp->devfn);
 			info->path[level].function = PCI_FUNC(tmp->devfn);
 			if (pci_is_root_bus(tmp->bus))