device/pci_device: Fix PCIe bridge detection

PCI bus 0 is not below any PCI device. In case of pci_domain_scan_bus(),
it's our virtual `domain` device.

Expecting a PCI device above bus 0 resulted in undefined behavior for
all boards with PCI. Only boards with a PCI device 00:00.0 that looked
like a PCIe bridge showed issues, though (e.g. OCP/DeltaLake).

Change-Id: I1fd68b9dc0d2e388ec2bbba4adbadd33e14f0171
Signed-off-by: Nico Huber <nico.h@gmx.de>
Fixes: commit 777ffff442 (device/pci_device.c: Scan only one device for PCIe)
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62376
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/device/pci_device.c

@@ -1352,6 +1352,9 @@ static bool pci_bus_only_one_child(struct bus *bus)
 	if (!bridge)
 		return false;
 
+	if (bridge->path.type != DEVICE_PATH_PCI)
+		return false;
+
 	pcie_pos = pci_find_capability(bridge, PCI_CAP_ID_PCIE);
 	if (!pcie_pos)
 		return false;