of: Add vendor prefix for On Tat Industrial Company.

This is the vendor for a 7" DPI panel sold by Adafruit which I'd like
to describe in DT.
Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -172,6 +172,7 @@ nxp	NXP Semiconductors
 okaya	Okaya Electric America, Inc.
 olimex	OLIMEX Ltd.
 onnn	ON Semiconductor Corp.
+ontat	On Tat Industrial Company
 opencores	OpenCores.org
 option	Option NV
 ortustech	Ortus Technology Co., Ltd.