siox: make siox_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 siox_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>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Thorsten Scherer <t.scherer@eckelmann.de>
Link: https://lore.kernel.org/r/20240204-bus_cleanup-siox-v2-1-3813a6a55dcc@marliere.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/siox/siox-core.c

@@ -543,7 +543,7 @@ static void siox_shutdown(struct device *dev)
 		sdriver->shutdown(sdevice);
 }
 
-static struct bus_type siox_bus_type = {
+static const struct bus_type siox_bus_type = {
 	.name = "siox",
 	.match = siox_match,
 	.probe = siox_probe,