spi: dt-bindings: nuvoton,wpcm450-fiu: Fix error in example (bogus include)

The nuvoton,wpcm450-fiu binding's example includes
nuvoton,wpcm450-clk.h, which has not been merged yet,
thus causing a dt_binding_check error on -next.

Fix this error by simply hardcoding the clock index in the example,
before the breakage spreads any further.

Fixes: dd71cd4dd6 ("spi: Add Nuvoton WPCM450 Flash Interface Unit (FIU) bindings")
Reported-by: Rob Herring <robh@kernel.org>
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221129102225.3598044-2-j.neuschaefer@gmx.net
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/nuvoton,wpcm450-fiu.yaml

@@ -45,14 +45,13 @@ unevaluatedProperties: false
 
 examples:
   - |
-    #include <dt-bindings/clock/nuvoton,wpcm450-clk.h>
     spi@c8000000 {
       compatible = "nuvoton,wpcm450-fiu";
       reg = <0xc8000000 0x1000>, <0xc0000000 0x4000000>;
       #address-cells = <1>;
       #size-cells = <0>;
       reg-names = "control", "memory";
-      clocks = <&clk WPCM450_CLK_FIU>;
+      clocks = <&clk 0>;
       nuvoton,shm = <&shm>;
 
       flash@0 {