device/root_device: Consolidate common _scan_bus() functions

scan_usb_bus() and root_dev_scan_bus() had the very same implementation.
So rename the latter to scan_static_bus() and use that for both cases.

Change-Id: If0aba9c690b23e3716f2d47ff7a8c3e8f6d82679
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/31901
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/drivers/usb/acpi/usb_acpi.c

@@ -85,7 +85,7 @@ static struct device_operations usb_acpi_ops = {
 	.read_resources			= DEVICE_NOOP,
 	.set_resources			= DEVICE_NOOP,
 	.enable_resources		= DEVICE_NOOP,
-	.scan_bus			= scan_usb_bus,
+	.scan_bus			= scan_static_bus,
 	.acpi_fill_ssdt_generator	= usb_acpi_fill_ssdt_generator,
 };