clk: meson: meson8b: set audio output clock hierarchy

The aiu devices peripheral clocks needs the aiu and aiu_glue clocks to
operate. Reflect this hierarchy in the clock tree.

Fixes: e31a1900

 ("meson: clk: Add support for clock gates")
Suggested-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>