soundwire: constify the struct device_type usage

Since commit aed65af1cc2f ("drivers: make device_type const"), the driver
core can properly handle constant struct device_type. Move the
sdw_master_type and sdw_slave_type variables to be constant structures as
well, placing it into read-only memory which can not be modified at
runtime.

Cc: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: "Ricardo B. Marliere" <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/soundwire/master.c

···
 			   pm_generic_runtime_resume, NULL)
 };
 
-struct device_type sdw_master_type = {
+const struct device_type sdw_master_type = {
 	.name =		"soundwire_master",
 	.release =	sdw_master_device_release,
 	.pm = &master_dev_pm,

drivers/soundwire/slave.c

···
 	kfree(slave);
 }
 
-struct device_type sdw_slave_type = {
+const struct device_type sdw_slave_type = {
 	.name =		"sdw_slave",
 	.release =	sdw_slave_release,
 	.uevent =	sdw_slave_uevent,

include/linux/soundwire/sdw_type.h

···
 #define __SOUNDWIRE_TYPES_H
 
 extern const struct bus_type sdw_bus_type;
-extern struct device_type sdw_slave_type;
-extern struct device_type sdw_master_type;
+extern const struct device_type sdw_slave_type;
+extern const struct device_type sdw_master_type;
 
 static inline int is_sdw_slave(const struct device *dev)
 {