powerpc: ibmebus: make ibmebus_bus_type const

Since commit d492cc25 ("driver core: device.h: make struct
bus_type a const *"), the driver core can properly handle constant
struct bus_type, move the ibmebus_bus_type variable to be a constant
structure as well, placing it into read-only memory which can not be
modified at runtime.
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Ricardo B. Marliere" <ricardo@marliere.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240212-bus_cleanup-powerpc2-v2-5-8441b3f77827@marliere.net

arch/powerpc/include/asm/ibmebus.h

@@ -48,7 +48,7 @@
 
 struct platform_driver;
 
-extern struct bus_type ibmebus_bus_type;
+extern const struct bus_type ibmebus_bus_type;
 
 int ibmebus_register_driver(struct platform_driver *drv);
 void ibmebus_unregister_driver(struct platform_driver *drv);

arch/powerpc/platforms/pseries/ibmebus.c

@@ -55,7 +55,7 @@ static struct device ibmebus_bus_device = { /* fake "parent" device */
 	.init_name = "ibmebus",
 };
 
-struct bus_type ibmebus_bus_type;
+const struct bus_type ibmebus_bus_type;
 
 /* These devices will automatically be added to the bus during init */
 static const struct of_device_id ibmebus_matches[] __initconst = {
@@ -432,7 +432,7 @@ static int ibmebus_bus_modalias(const struct device *dev, struct kobj_uevent_env
 	return of_device_uevent_modalias(dev, env);
 }
 
-struct bus_type ibmebus_bus_type = {
+const struct bus_type ibmebus_bus_type = {
 	.name      = "ibmebus",
 	.uevent    = ibmebus_bus_modalias,
 	.bus_groups = ibmbus_bus_groups,