ASoC: sh: fsi: make sure fsi_stream_push/pop access by spin lock

fsi_stream_push/pop might be called in same time.
This patch protect it.

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