mmc: jz4740: Work around bug on JZ4760(B)

On JZ4760 and JZ4760B, SD cards fail to run if the maximum clock
rate is set to 50 MHz, even though the controller officially does
support it.

Until the actual bug is found and fixed, limit the maximum clock rate to
24 MHz.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230131210229.68129-1-paul@crapouillou.net


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>