ASoC: fsl_spdif: Reduce the noise on comments

Remove the "====" pattern to let the comments cleaner and more uniform.

Also, do not use multi-line style for a single line comment.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Nicolin Chen <b42378@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>