mmc: host: renesas_sdhi: Fix the actual clock

mmc: host: renesas_sdhi: Fix the actual clock

Wrong actual clock reported, if the SD clock division ratio is other
than 1:1(bits DIV[7:0] in SD_CLK_CTRL are set to 11111111).

On high speed mode, cat /sys/kernel/debug/mmc1/ios
Without the patch:
clock:          50000000 Hz
actual clock:   200000000 Hz

After the fix:
clock:          50000000 Hz
actual clock:   50000000 Hz

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20250629203859.170850-1-biju.das.jz@bp.renesas.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>