ASoC: rsnd: tidyup SSI interrupt enable/disable method

Current SSI doesn't care interrupt "disable" method. And, it is used
when PIO mode only at this point. SSI interrupt will be used for
sound R/L issue workaround when DMA mode too.
This patch tidyup SSI interrupt enable/disable method.

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