ASoC: mmp-sspa: Prepare/unprepare the clocks

The driver enables the clocks without preparing them and disables
without unpreparing afterwards. Fix that.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20200511210134.1224532-8-lkundrak@v3.sk


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