ASoC: fsi: modify fsi_pio_get_area() parameter and using position

This patch modify fsi_pio_get_area() parameter to use
struct fsi_stream, and used it on fsi_fifo_data_ctrl().
This is just prepare cleanup for DMAEngine support.

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