ASoC: fsl_sai: Update slots number according to bclk_ratio

The bclk_ratio is set by .set_bclk_ratio API.
bclk_ratio = slots * slot_width
So if slots is not set by .set_tdm_slot, then it can be calculated
by bclk_ratio.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1659681926-13493-1-git-send-email-shengjiu.wang@nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>