platform: x86: ibm_rtl: make rtl_subsys const

Now that the driver core can properly handle constant struct bus_type,
move the rtl_subsys variable to be a constant structure as well,
placing it into read-only memory which can not be modified at runtime.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Ricardo B. Marliere" <ricardo@marliere.net>
Link: https://lore.kernel.org/r/20240204-bus_cleanup-platform-drivers-x86-v1-2-1f0839b385c6@marliere.netReviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

drivers/platform/x86/ibm_rtl.c

@@ -179,7 +179,7 @@ static ssize_t rtl_set_state(struct device *dev,
 	return ret;
 }
 
-static struct bus_type rtl_subsys = {
+static const struct bus_type rtl_subsys = {
 	.name = "ibm_rtl",
 	.dev_name = "ibm_rtl",
 };