ASoC: rcar: avoid SSI_MODEx settings for SSI8

SSI8 is is sharing pin with SSI7, and nothing to do for SSI_MODEx.
It is special pin and it needs special settings whole system,
but we can't confirm it, because we never have SSI8 available board.

This patch fixup SSI_MODEx settings error for SSI8 on connection test,
but should be confirmed behavior on real board in the future.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>