PNP: make pnp_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the pnp_bus_type variable to be a constant structure as well,
placing it into read-only memory which can not be modified at runtime.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/pnp/driver.c

@@ -256,7 +256,7 @@ static const struct dev_pm_ops pnp_bus_dev_pm_ops = {
 	.restore = pnp_bus_resume,
 };
 
-struct bus_type pnp_bus_type = {
+const struct bus_type pnp_bus_type = {
 	.name    = "pnp",
 	.match   = pnp_bus_match,
 	.probe   = pnp_device_probe,

include/linux/pnp.h

@@ -435,7 +435,7 @@ struct pnp_protocol {
 #define protocol_for_each_dev(protocol, dev)	\
 	list_for_each_entry(dev, &(protocol)->devices, protocol_list)
 
-extern struct bus_type pnp_bus_type;
+extern const struct bus_type pnp_bus_type;
 
 #if defined(CONFIG_PNP)