devicetree: Add msi to the vendor-prefix list

Document the the "msi" (Micro-Star International Co. Ltd.) vendor prefix
which is used in sun6i-a31s-primo81.dts.
Signed-off-by: Karsten Merker <merker@debian.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -135,6 +135,7 @@ mitsubishi	Mitsubishi Electric Corporation
 mosaixtech	Mosaix Technologies, Inc.
 moxa	Moxa
 mpl	MPL AG
+msi	Micro-Star International Co. Ltd.
 mti	Imagination Technologies Ltd. (formerly MIPS Technologies Inc.)
 mundoreader	Mundo Reader S.L.
 murata	Murata Manufacturing Co., Ltd.