of: Add vendor prefix for Lattice Semiconductor

Lattice Semiconductor Corporation is a manufacturer of integrated
circuits and IP products, including low-power FPGAs, video connectivity
devices and millimeter wave wireless products.

Website: http://latticesemi.com

Signed-off-by: Joel Holdsworth <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Acked-by: Moritz Fischer <[e-mail]>
Signed-off-by: Alan Tull <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/vendor-prefixes.txt

···
 kyo	Kyocera Corporation
 lacie	LaCie
 lantiq	Lantiq Semiconductor
+lattice	Lattice Semiconductor
 lego	LEGO Systems A/S
 lenovo	Lenovo Group Ltd.
 lg	LG Corporation