ASoC: rsnd: ADG uses mod base common method

Renesas sound has ADG IP, but it is special device.
(It is clock generater, and it doesn't need MSTP)
Thus, ADG didn't use mod base common method on rsnd driver.
But it can be confusable point. Let's use common method

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