[efi] Return only registered EFI devices from efidev_parent()

efidev_parent() currently assumes that any device with BUS_TYPE_EFI is
part of a struct efi_device.  This assumption is not valid, since the
code in efi_device_info() may also create a device with BUS_TYPE_EFI.

Fix by searching through the list of registered EFI devices when
looking for a match, instead of relying on the bus type value.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/interface/efi/efi_driver.c

  */
 struct efi_device * efidev_parent ( struct device *dev ) {
 	struct device *parent;
+	struct efi_device *efidev;
 
-	/* Walk upwards until we find an EFI device */
+	/* Walk upwards until we find a registered EFI device */
 	while ( ( parent = dev->parent ) ) {
-		if ( parent->desc.bus_type == BUS_TYPE_EFI )
-			return container_of ( parent, struct efi_device, dev );
+		list_for_each_entry ( efidev, &efi_devices, dev.siblings ) {
+			if ( parent == &efidev->dev )
+				return efidev;
+		}
 		dev = parent;
 	}