firmware: arm_scmi: Make scmi_bus_type const

Now that the driver core can properly handle constant struct bus_type,
move the scmi_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: Cristian Marussi <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Sudeep Holla <[e-mail]>

drivers/firmware/arm_scmi/bus.c

···
 		scmi_drv->remove(scmi_dev);
 }
 
-struct bus_type scmi_bus_type = {
+const struct bus_type scmi_bus_type = {
 	.name =	"scmi_protocol",
 	.match = scmi_dev_match,
 	.probe = scmi_dev_probe,

drivers/firmware/arm_scmi/common.h

···
 void scmi_setup_protocol_implemented(const struct scmi_protocol_handle *ph,
 				     u8 *prot_imp);
 
-extern struct bus_type scmi_bus_type;
+extern const struct bus_type scmi_bus_type;
 
 #define SCMI_BUS_NOTIFY_DEVICE_REQUEST		0
 #define SCMI_BUS_NOTIFY_DEVICE_UNREQUEST	1