Operations to unflatten fdt blobs never modify the input blobs, hence
make them const. Now we no longer need to cast arbitrary const data to
"void *" when calling of_fdt_unflatten_tree().
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NRob Herring <robh@kernel.org>