mmc: mtk-sd: Improve data type in msdc_timeout_cal()

mmc: mtk-sd: Improve data type in msdc_timeout_cal()

The local variable clk_ns uses at most 32 bits and can be a u32.

Replace the 64-by-32 do_div() division with a standard divison.

Since do_div() casts the divisor to u32 anyway, changing the data type
of clk_ns to u32 also removes the following Coccinelle/coccicheck
warning reported by do_div.cocci:

  WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead

Use min_t(u32,,) to simplify the code and improve its readability.

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Link: https://lore.kernel.org/r/20240818142300.64156-2-thorsten.blum@toblux.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>