ASoC: omap-pcm: No need to set constraint at open time

The same constraint is going to be set in the snd_dmaengine_pcm_open()
function, so there is no need to set it here as well.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>