device-dax: make dax_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the dax_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/20240204-bus_cleanup-dax-v1-1-69a6e4a8553b@marliere.netSigned-off-by: Dave Jiang <dave.jiang@intel.com>

drivers/dax/bus.c

@@ -222,7 +222,7 @@ static void dax_bus_remove(struct device *dev)
 		dax_drv->remove(dev_dax);
 }
 
-static struct bus_type dax_bus_type = {
+static const struct bus_type dax_bus_type = {
 	.name = "dax",
 	.uevent = dax_bus_uevent,
 	.match = dax_bus_match,