rockchip: clk: remove RATE_TO_DIV

Use DIV_ROUND_UP instead RATE_TO_DIV for all Rockchip SoC
clock driver.
Add or fix the div-field overflow check at the same time.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>