of/fdt: Document detached argument to __unflatten_device_tree()

This wasn't documented.

Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Reviewed-by: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/fdt.c

@@ -437,6 +437,7 @@ static int unflatten_dt_nodes(const void *blob,
  * @mynodes: The device_node tree created by the call
  * @dt_alloc: An allocator that provides a virtual address to memory
  * for the resulting tree
+ * @detached: if true set OF_DETACHED on @mynodes
  *
  * Returns NULL on failure or the memory chunk containing the unflattened
  * device tree on success.