clockevents: Make clockevents_subsys const

Now that the driver core can properly handle constant struct bus_type,
move the clockevents_subsys 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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240204-bus_cleanup-time-v1-2-207ec18e24b8@marliere.net

kernel/time/clockevents.c

@@ -659,7 +659,7 @@ void tick_cleanup_dead_cpu(int cpu)
 #endif
 
 #ifdef CONFIG_SYSFS
-static struct bus_type clockevents_subsys = {
+static const struct bus_type clockevents_subsys = {
 	.name		= "clockevents",
 	.dev_name       = "clockevent",
 };