ASoC: rsnd: rsnd_scu_hpbif_is_enable() become macro

rsnd_scu_hpbif_is_enable() is used only scu.c now.
It can be local macro

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