dio: make dio_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the dio_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/20240212-bus_cleanup-dio-v2-1-3b1ba4c0547d@marliere.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/dio/dio-driver.c

@@ -123,7 +123,7 @@ static int dio_bus_match(struct device *dev, struct device_driver *drv)
 }
 
 
-struct bus_type dio_bus_type = {
+const struct bus_type dio_bus_type = {
 	.name	= "dio",
 	.match	= dio_bus_match,
 	.probe	= dio_device_probe,

include/linux/dio.h

@@ -68,7 +68,7 @@ struct dio_bus {
 };
 
 extern struct dio_bus dio_bus;      /* Single DIO bus */
-extern struct bus_type dio_bus_type;
+extern const struct bus_type dio_bus_type;
 
     /*
      *  DIO device IDs