of: Add vendor prefix for Digi International Inc.

Using "digi" for Digi International Inc.
Additionally, this patch keep "dlink" entry sorted alphabetically.
Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -35,6 +35,7 @@ crystalfontz	Crystalfontz America, Inc.
 dallas	Maxim Integrated Products (formerly Dallas Semiconductor)
 davicom	DAVICOM Semiconductor, Inc.
 denx	Denx Software Engineering
+digi	Digi International Inc.
 dlink	D-Link Corporation
 dmo	Data Modul AG
 edt	Emerging Display Technologies