ASoC: OMAP: HDMI: Initialize IEC-60958 channel status word

As the IEC-60958 channel status word is set by ANDing and ORing with
the appropriate definitions, the word bytes need to be initialized
to zero to avoid misconfiguration due to previous hw_params calls.

Signed-off-by: Ricardo Neri <rneri@dextratech.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>