ASoC: fsl: Add the audio interface acronyms in Kconfig text

To keep consistency with the other Kconfig entries, use the audio
interface acronyms (SSI and SPDIF) in the Kconfig menu text.

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