ASoC: fsl_audmix: Add spin lock to protect tdms

Audmix support two substream, When two substream start
to run, the trigger function may be called by two substream
in same time, that the priv->tdms may be updated wrongly.

The expected priv->tdms is 0x3, but sometimes the
result is 0x2, or 0x1.

Fixes: be1df61c

 ("ASoC: fsl: Add Audio Mixer CPU DAI driver")
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/1e706afe53fdd1fbbbc79277c48a98f8416ba873.1573458378.git.shengjiu.wang@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: <stable@vger.kernel.org>