i2c: Fix sparse warning in i2c.h

Kill a sparse warning by un-nesting two container_of() calls.
    
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

include/linux/i2c.h

@@ -185,7 +185,8 @@ struct i2c_client {
 
 static inline struct i2c_client *kobj_to_i2c_client(struct kobject *kobj)
 {
-	return to_i2c_client(container_of(kobj, struct device, kobj));
+	struct device * const dev = container_of(kobj, struct device, kobj);
+	return to_i2c_client(dev);
 }
 
 static inline void *i2c_get_clientdata (struct i2c_client *dev)