ASoC: rcar: remove .path_init/exit from rsnd_gen_ops

rsnd_gen_ops has .path_init/exit callback function
which cares SRU/SSI (if Gen1) SCU/SSIU/SSI (if Gen2)
path settings.
But, the differences between Gen1/Gen2 are cared
in ssi.c/scu.c, and the path itself is same in Gen1/Gen2.
This patch removes .path_init/exit callback.

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