ASoC: max98088: fix ni clock divider calculation

The ni1/ni2 ratio formula [1] uses the pclk which is the prescaled mclk.
The max98088 datasheet [2] has no such formula but table-12 equals so
we can assume that it is the same for both devices.

While on it make use of DIV_ROUND_CLOSEST_ULL().

[1] https://datasheets.maximintegrated.com/en/ds/MAX98089.pdf; page 86
[2] https://datasheets.maximintegrated.com/en/ds/MAX98088.pdf; page 82

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Link: https://lore.kernel.org/r/20210423135402.32105-1-m.felsch@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>