dt-bindings: thermal: add file extension to brcm,ns-thermal

Add the missing .txt extension to the Broadcom Northstar binding document.

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Signed-off-by: Rob Herring <robh@kernel.org>

diff --git a/Documentation/devicetree/bindings/thermal/brcm,ns-thermal b/Documentation/devicetree/bindings/thermal/brcm,ns-thermal.txt
similarity index 100%
rename from Documentation/devicetree/bindings/thermal/brcm,ns-thermal
rename to Documentation/devicetree/bindings/thermal/brcm,ns-thermal.txt