gpu: host1x: bus: make host1x_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 host1x_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>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240213-bus_cleanup-host1x-v1-1-54ec51b5d14f@marliere.net

drivers/gpu/host1x/bus.c

@@ -365,7 +365,7 @@ static const struct dev_pm_ops host1x_device_pm_ops = {
 	.restore = pm_generic_restore,
 };
 
-struct bus_type host1x_bus_type = {
+const struct bus_type host1x_bus_type = {
 	.name = "host1x",
 	.match = host1x_device_match,
 	.uevent = host1x_device_uevent,

drivers/gpu/host1x/bus.h

@@ -10,7 +10,7 @@
 struct bus_type;
 struct host1x;
 
-extern struct bus_type host1x_bus_type;
+extern const struct bus_type host1x_bus_type;
 
 int host1x_register(struct host1x *host1x);
 int host1x_unregister(struct host1x *host1x);