mmc: sdhci-sprd: Fix the limitation of div

Because the bit field size of the divider coefficient register is 1023, it is
limited before returning the value.

Signed-off-by: Wenchao Chen <wenchao.chen@unisoc.com>
Link: https://lore.kernel.org/r/20220914063702.20283-1-wenchao.chen666@gmail.com


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