i2c: constify the struct device_type usage

Since commit aed65af1 ("drivers: make device_type const"), the driver
core can properly handle constant struct device_type. Move the
i2c_adapter_type and i2c_client_type variables to be constant structures as
well, placing it into read-only memory which can not be modified at
runtime.
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

drivers/i2c/i2c-core-base.c

@@ -701,7 +701,7 @@ const struct bus_type i2c_bus_type = {
 };
 EXPORT_SYMBOL_GPL(i2c_bus_type);
 
-struct device_type i2c_client_type = {
+const struct device_type i2c_client_type = {
 	.groups		= i2c_dev_groups,
 	.uevent		= i2c_device_uevent,
 	.release	= i2c_client_dev_release,
@@ -1343,7 +1343,7 @@ static struct attribute *i2c_adapter_attrs[] = {
 };
 ATTRIBUTE_GROUPS(i2c_adapter);
 
-struct device_type i2c_adapter_type = {
+const struct device_type i2c_adapter_type = {
 	.groups		= i2c_adapter_groups,
 	.release	= i2c_adapter_dev_release,
 };

include/linux/i2c.h

@@ -24,8 +24,8 @@
 #include <uapi/linux/i2c.h>
 
 extern const struct bus_type i2c_bus_type;
-extern struct device_type i2c_adapter_type;
-extern struct device_type i2c_client_type;
+extern const struct device_type i2c_adapter_type;
+extern const struct device_type i2c_client_type;
 
 /* --- General options ------------------------------------------------	*/