Some devfreq consumers like UFS driver need to work with multiple clocks
through the OPP framework. For this reason, OPP framework exposes the
_indexed() APIs for finding the floor/ceil of the supplied frequency of
the indexed clock. So let's use them in the devfreq driver.

Currently, the clock index of 0 is used which works fine for multiple as
well as single clock.

Link: https://lore.kernel.org/all/20231003111232.42663-3-manivannan.sadhasivam@linaro.org/Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>