spi: s3c64xx: add no_cs description

This patch adds missing variable no_cs descriptions.

Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Andi Shyti <andi@etezian.org>
Link: https://lore.kernel.org/r/20230306014239.80570-1-jaewon02.kim@samsung.com
Signed-off-by: Mark Brown <broonie@kernel.org>