spi: bcm-qspi: Mark OF related data as maybe unused

spi: bcm-qspi: Mark OF related data as maybe unused

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

  drivers/spi/spi-bcm-qspi.c:1460:34: error: ‘bcm_qspi_of_match’ defined but not used [-Werror=unused-const-variable=]

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20230310222857.315629-13-krzysztof.kozlowski@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>