ASoC: fsi: don't use platform info pointer on probe()

Current FSI driver is using platform info pointer,
but it is not good design for DT support.
This patch made it not to use platform info pointer.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>