ASoC: rsnd: rename SSI function name of PIO

Current R-Car sound SSI PIO/DMA mode are using interrupt.
it is no longer "xxx_pio_xxx", rename it.

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