dt-bindings: brcm,avs-ro-thermal: Fix binding check issues

Drop the reg property since this only necessary for the parent and
add the missing thermal-sensor-cells property description.
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Fixes: 37e9cc08e9678 ("dt-bindings: Add Broadcom AVS RO thermal")
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1579200077-17496-1-git-send-email-stefan.wahren@i2se.com

Documentation/devicetree/bindings/thermal/brcm,avs-ro-thermal.yaml

@@ -23,12 +23,15 @@ properties:
   compatible:
     const: brcm,bcm2711-thermal
 
-  reg:
-    maxItems: 1
+  # See ./thermal.txt for details
+  "#thermal-sensor-cells":
+    const: 0
 
 required:
   - compatible
-  - reg
+  - '#thermal-sensor-cells'
+
+additionalProperties: false
 
 examples:
   - |