ASoC: renesas: rsnd: enable to use "adg" clock

ADG needs its MSTP to use it, and it was handled as "clk_i" before.
R-Car Gen2/Gen3 are using it, but Gen4 doesn't have it.
"clk_i" is not intuitive for ADG MSTP.
Let's enable to use "adg" clock. It can keep compatible with R-Car
Gen2/Gen3 and Gen4.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://patch.msgid.link/87sem62x00.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>