mmc: sdhci-sprd: Disable CLK_AUTO when the clock is less than 400K

When the clock is less than 400K, some SD cards fail to initialize
because CLK_AUTO is enabled.

Fixes: fb8bd90f

 ("mmc: sdhci-sprd: Add Spreadtrum's initial host controller")
Signed-off-by: Wenchao Chen <wenchao.chen@unisoc.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20221207051909.32126-1-wenchao.chen@unisoc.com


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