Renesas sound driver can output Audio-clkout0/1/2/3,
but these are optional properties for each board.
Reported-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NKuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: NMark Brown <broonie@kernel.org>