ASoC: audio-graph-scu-card: use asoc_simple_card_of_parse_routing()

Current simple/audio scu card drivers are supporting same
routing on DT, but, doesn't use same function for it.
Encapsulation is one of simple card util's purpose.
Let's use asoc_simple_card_of_parse_routing

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