ASoC: kirkwood: Fix erroneous double output while playing

This patch fixes the setting of the register KIRKWOOD_PLAYCTL which did
always streaming on both I2S and SPDIF, ignoring the DAI ID.

The bug was introduced by the commit 75b9b65e
 "ASoC: kirkwood: add S/PDIF support"

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mark Brown <broonie@linaro.org>