spi: s3c64xx: extend description of compatible's fifo_depth

The FIFO depth specified with the compatibles's data is used where all
the instances of the IP define the same FIFO depth. It naturally has
higher precedence than the FIFO depth specified via DT. Specifying FIFO
depth in DT becomes superfluous in this case. Extend comment about
compatible's FIFO depth.

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://patch.msgid.link/20250214-spi-s3c64xx-fifo-depth-v1-1-e1b1915e3ee7@linaro.org


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