ASoC: fsl_spdif: Clear the validity bit for TX

In IEC958 spec, "The validity bit is logical "0" if the
information in the main data field is reliable, and it
is logical "1" if it is not".

The default value of "ValCtrl" is zero, which means
"Outgoing Validity always set", then all the data is not
reliable, then some spdif sink device will drop the data.

So set "ValCtrl" to 1, that is to clear "Outgoing Validity"
in default.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1594112066-31297-2-git-send-email-shengjiu.wang@nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>