ASoC: simple-card-utils: check "reg" property on asoc_simple_card_get_dai_id()

We will get DAI ID from "reg" property if it has on DT, otherwise get
it by counting port/endpoint.

But in below case, we need to get DAI ID = 0 via port reg = <0>, but
current implementation returns ID = 1, because it can't judge ID = 0 was
from "non reg" or "reg = <0>".
Thus, it will count port/endpoint number as "non reg" case.

of_graph_parse_endpoint() implementation itself is not a problem,
but because asoc_simple_card_get_dai_id() need to count port/endpoint
number when "non reg" case, it need to know ID = 0 was from
"non reg" or "reg = <0>".
This patch fix this issue.

	port {
		reg = <0>;
		xxxx: endpoint@0 {
		};
=>		xxxx: endpoint@1 {
		};
	};

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