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

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: dd71cd4dd6c9b ("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>