of: wrap accesses to device_node kobject

In preparation to make kobject element in struct device_node optional,
provide and use a macro to return the kobject pointer. The only user
outside the DT core is the driver core.
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Tested-by: Nicolas Pitre <nico@linaro.org>
Reviewed-by: Frank Rowand <frowand.list@gmail.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/base/core.c

@@ -1571,7 +1571,7 @@ static int device_add_class_symlinks(struct device *dev)
 	int error;
 
 	if (of_node) {
-		error = sysfs_create_link(&dev->kobj, &of_node->kobj,"of_node");
+		error = sysfs_create_link(&dev->kobj, of_node_kobj(of_node), "of_node");
 		if (error)
 			dev_warn(dev, "Error %d creating of_node link\n",error);
 		/* An error here doesn't warrant bringing down the device */

include/linux/of.h

@@ -111,6 +111,8 @@ static inline void of_node_init(struct device_node *node)
 	node->fwnode.ops = &of_fwnode_ops;
 }
 
+#define of_node_kobj(n) (&(n)->kobj)
+
 /* true when node is initialized */
 static inline int of_node_is_initialized(struct device_node *node)
 {