mmc: dw_mmc: change the DW_MCI_FREQ_MIN from 400K to 100K

If there is no property "clock-freq-min-max", mmc->f_min should be set
to 400K by default. But Some SoC can be used 100K.
When 100K is used, MMC core will try to check from 400K to 100K.

Reported-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>