drm: display: make dp_aux_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the dp_aux_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: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20240203-bus_cleanup-gpu-v1-1-1b6ecdb5f941@marliere.netSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240203-bus_cleanup-gpu-v1-1-1b6ecdb5f941@marliere.net

drivers/gpu/drm/display/drm_dp_aux_bus.c

@@ -127,7 +127,7 @@ static void dp_aux_ep_shutdown(struct device *dev)
 		aux_ep_drv->shutdown(to_dp_aux_ep_dev(dev));
 }
 
-static struct bus_type dp_aux_bus_type = {
+static const struct bus_type dp_aux_bus_type = {
 	.name		= "dp-aux",
 	.match		= dp_aux_ep_match,
 	.probe		= dp_aux_ep_probe,