mmc: sdhci-sprd: Fix minimum clock limit

The Spreadtrum controller supports 100KHz minimal clock rate, which means
that the current value 400KHz is wrong.

Unfortunately this has also lead to fail to initialize some cards, which
are allowed to require 100KHz to work. So, let's fix the problem by
changing the minimal supported clock rate to 100KHz.

Signed-off-by: Wenchao Chen <wenchao.chen@unisoc.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Fixes: fb8bd90f ("mmc: sdhci-sprd: Add Spreadtrum's initial host controller")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20221011104935.10980-1-wenchao.chen666@gmail.com


[Ulf: Clarified to commit-message]
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>