staging: pi433: overlay: Convert to sugar syntax

Using overlay sugar syntax makes the DTS overlay files easier to read
(and write).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200221122133.32024-4-geert+renesas@glider.be


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>