dt-bindings: add vendor prefix for Dioo

Dioo (http://http://www.dioo.com) design and produce power analog and
mixed signal IC.
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -79,6 +79,7 @@ denx	Denx Software Engineering
 devantech	Devantech, Ltd.
 digi	Digi International Inc.
 digilent	Diglent, Inc.
+dioo	Dioo Microcircuit Co., Ltd
 dlg	Dialog Semiconductor
 dlink	D-Link Corporation
 dmo	Data Modul AG