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 <[e-mail]>
Suggested-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: "Ricardo B. Marliere" <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/dio/dio-driver.c

···
 }
 
 
-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

···
 };
 
 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