dt-bindings: Add Western Digital to vendor prefixes

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -260,6 +260,7 @@ via	VIA Technologies, Inc.
 virtio	Virtual I/O Device Specification, developed by the OASIS consortium
 vivante	Vivante Corporation
 voipac	Voipac Technologies s.r.o.
+wd	Western Digital Corp.
 wexler	Wexler
 winbond Winbond Electronics corp.
 wlf	Wolfson Microelectronics