driver core: soc: remove layering violation for the soc_bus

The soc_bus code pokes around in the internal bus structures assuming
that it "knows" if a field is not set that it has not been registered
yet. That isn't a safe assumption, so just remove the layering
violation entirely and keep track if the bus has been registered or not
ourselves.

Reviewed-by: Rafael J. Wysocki <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/soc.c

···
 static struct bus_type soc_bus_type = {
 	.name  = "soc",
 };
+static bool soc_bus_registered;
 
 static DEVICE_ATTR(machine,		0444, soc_info_show,  NULL);
 static DEVICE_ATTR(family,		0444, soc_info_show,  NULL);
···
 	const struct attribute_group **soc_attr_groups;
 	int ret;
 
-	if (!soc_bus_type.p) {
+	if (!soc_bus_registered) {
 		if (early_soc_dev_attr)
 			return ERR_PTR(-EBUSY);
 		early_soc_dev_attr = soc_dev_attr;
···
 	ret = bus_register(&soc_bus_type);
 	if (ret)
 		return ret;
+	soc_bus_registered = true;
 
 	if (early_soc_dev_attr)
 		return PTR_ERR(soc_device_register(early_soc_dev_attr));