devicetree: add vendor prefix for Winstar Display Corp.

Winstar Display Corp. is specialized in LCD displays for embedded
products.
cf: http://www.winstar.com.tw



Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>