ASoC: tegra: drop Kconfig description for SND_SOC_TEGRA_DAS

The DAS, I2S, and SPDIF Kconfig options are intended to be selected by
the Kconfig options for ASoC machine drivers. As such, they don't need
to be user-visible themselves. Drop the description from the DAS variable
to achieve this. I2S and SPDIF already don't have a description.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>