ASoC: fsi: ensures process inside master lock

Bit operation for fsi_master should be done inside master lock.
But soft-reset/interrupt operation were outside of it.
This patch modify this problem.
It still allow to INT_ST outside-operation on fsi_interrupt,
but it is not problem.
Because this register doesn't need the bit operation.

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