of: add vendor prefix for Silicon Storage Technology Inc.

Add Silicon Storage Technology Inc. to the list of devicetree
vendor prefixes.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -318,6 +318,7 @@ solomon        Solomon Systech Limited
 sony	Sony Corporation
 spansion	Spansion Inc.
 sprd	Spreadtrum Communications Inc.
+sst	Silicon Storage Technology, Inc.
 st	STMicroelectronics
 starry	Starry Electronic Technology (ShenZhen) Co., LTD
 startek	Startek