ASoC: atmel_ssc_dai: distinguish the different SSC

Cpu_dai id always equals 0, can't distinguish the
different SSC. Use platform_device id to record
and distinguish the different SSC.

Signed-off-by: Songjun Wu <songjun.wu@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>