spi: sh-msiof: Mark OF related data as maybe unused

The driver can be compile tested with !CONFIG_OF making certain data
unused:

  drivers/spi/spi-sh-msiof.c:1076:34: error: ‘sh_msiof_match’ defined but not used [-Werror=unused-const-variable=]

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230310222857.315629-14-krzysztof.kozlowski@linaro.org


Signed-off-by: Mark Brown <broonie@kernel.org>