dt-bindings: Add vendor prefix for Overkiz SAS

Overkiz is a smarthome solutions provider, more information on:
https://www.overkiz.com



Signed-off-by: Kamel Bouhara <kamel.bouhara@bootlin.com>
Link: https://lore.kernel.org/r/20191011125022.16329-2-kamel.bouhara@bootlin.com


Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>