dt-bindings: add rockchip vendor prefix

It seems I forgot to add the vendor prefix for rockchip to the vendor-prefix
list. Therefore add it now.
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -65,6 +65,7 @@ ralink	Mediatek/Ralink Technology Corp.
 ramtron	Ramtron International
 realtek Realtek Semiconductor Corp.
 renesas	Renesas Electronics Corporation
+rockchip	Fuzhou Rockchip Electronics Co., Ltd
 samsung	Samsung Semiconductor
 sbs	Smart Battery System
 schindler	Schindler