ASoC: fsl_spdif: Don't try to round-up for clock divisor calculation

As commit 6c8ca30e ("ASoC: fsl_ssi: Don't try to round-up for PM
divisor calculation") mentioned that there's no more need to use a
round up work around to get a better divisor since the clk-divider
driver has been refined a lot.

So this patch applies the same modification to fsl_spdif driver.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>