gpu: host1x: bus: make host1x_bus_type const

Since commit d492cc2573a0 ("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 <[e-mail]>
Suggested-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Ricardo B. Marliere <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/host1x/bus.c

···
 	.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

···
 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);