ASoC: tlv320dac33: Clearing FIFOFLUSH flag before playback

In repeated playback the FIFOFLUSH bit remained set, and
never has been cleared.
Clear it during the setup phase.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>