spi: s3c64xx: constify driver/match data

The match data (struct s3c64xx_spi_port_config) stored in of_device_id
and platform_device_id tables is not modified by the driver and can be
handled entirely in a const-way to increase the code safety.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Sylwester Nawrocki <snawrocki@kernel.org>
Link: https://lore.kernel.org/r/20210414203343.203119-3-krzysztof.kozlowski@canonical.com
Signed-off-by: Mark Brown <broonie@kernel.org>