devicetree: Add vendor prefix "mitsubishi" to vendor-prefixes.txt

Mitsubishi Electric Corporation has a numerical stock ticker, use the
company name as vendor prefix.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -83,6 +83,7 @@ maxim	Maxim Integrated Products
 mediatek	MediaTek Inc.
 micrel	Micrel Inc.
 microchip	Microchip Technology Inc.
+mitsubishi	Mitsubishi Electric Corporation
 mosaixtech	Mosaix Technologies, Inc.
 moxa	Moxa
 mpl	MPL AG