spi: s3c64xx: define a magic value

Define a magic value, it will be used in the next patch as well.

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Link: https://msgid.link/r/20240216070555.2483977-3-tudor.ambarus@linaro.org


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