dt-bindings: hwlock: sun6i: Add #hwlock-cells to example

The dt-bindings tools will compile the yaml dt examples
and this prevents an error about this node not existing.
Signed-off-by: Bastian Germann <bage@debian.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230215203711.6293-3-bage@debian.org

Documentation/devicetree/bindings/hwlock/allwinner,sun6i-a31-hwspinlock.yaml

@@ -48,5 +48,6 @@ examples:
         reg = <0x01c18000 0x1000>;
         clocks = <&ccu CLK_BUS_SPINLOCK>;
         resets = <&ccu RST_BUS_SPINLOCK>;
+        #hwlock-cells = <1>;
     };
 ...