ASoC: omap-mcpdm: Move the WD enable write inside omap_mcpdm_open_streams()

The DS4_WD_EN bit is only touched before calling omap_mcpdm_open_streams().
Move it inside of that function for simplicity.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>