s390/cio: make scm_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the scm_bus_type 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>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240203-bus_cleanup-s390-v1-4-ac891afc7282@marliere.netSigned-off-by: Heiko Carstens <hca@linux.ibm.com>

drivers/s390/cio/scm.c

@@ -42,7 +42,7 @@ static int scmdev_uevent(const struct device *dev, struct kobj_uevent_env *env)
 	return add_uevent_var(env, "MODALIAS=scm:scmdev");
 }
 
-static struct bus_type scm_bus_type = {
+static const struct bus_type scm_bus_type = {
 	.name  = "scm",
 	.probe = scmdev_probe,
 	.remove = scmdev_remove,