of: make of_device_make_bus_id() static

of_device_make_bus_id() was changed to non-static by commit c66012253800
("of/device: Make of_device_make_bus_id() usable by other code") more than
6 years ago, but there are no users of it outside of platform.c.  Make the
function static again.

Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>
diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index b8064bc..5dfcc96 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -76,7 +76,7 @@ EXPORT_SYMBOL(of_find_device_by_node);
  * derive a unique name. If it cannot, then it will prepend names from
  * parent nodes until a unique name can be derived.
  */
-void of_device_make_bus_id(struct device *dev)
+static void of_device_make_bus_id(struct device *dev)
 {
 	struct device_node *node = dev->of_node;
 	const __be32 *reg;