ASoC: Convert tegra_spdif to use module_platform_driver()

Use the module_platform_driver() macro which makes
the code smaller and a bit simpler.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>