DT: Add vendor prefix for Spansion Inc.

This is already in active use in several DTS files.
Signed-off-by: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -81,6 +81,7 @@ silabs	Silicon Laboratories
 simtek
 sirf	SiRF Technology, Inc.
 snps 	Synopsys, Inc.
+spansion	Spansion Inc.
 st	STMicroelectronics
 ste	ST-Ericsson
 stericsson	ST-Ericsson