ASoC: rsnd: has .symmetric_rates if SSIs are sharing WS pin

If SSIs are sharing WS pin, it should has .symmetric_rates.
This patch sets it.

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>