of: Add vendor prefix for Advantech Corporation

This patch adds vendor prefix for Advantech Corporation.
Website: http://www.advantech.com/Signed-off-by: Akshay Bhat <akshay.bhat@timesys.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -10,6 +10,7 @@ ad	Avionic Design GmbH
 adapteva	Adapteva, Inc.
 adh	AD Holdings Plc.
 adi	Analog Devices, Inc.
+advantech	Advantech Corporation
 aeroflexgaisler	Aeroflex Gaisler AB
 al	Annapurna Labs
 allwinner	Allwinner Technology Co., Ltd.