dt-bindings: Add vendor prefix for Adaptrum, Inc.

Adaptrum is a manufacturer of TV White Space (TVWS) wireless
technology. Using dynamic spectrum access to deliver affordable
internet connectivity over non-line-of-sight (NLOS) fixed wireless,
Adaptrum is helping close the digital divide worldwide.
Signed-off-by: Alexandru Gagniuc <alex.g@adaptrum.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -9,6 +9,7 @@ actions	Actions Semiconductor Co., Ltd.
 active-semi	Active-Semi International Inc
 ad	Avionic Design GmbH
 adapteva	Adapteva, Inc.
+adaptrum	Adaptrum, Inc.
 adh	AD Holdings Plc.
 adi	Analog Devices, Inc.
 advantech	Advantech Corporation