clk: meson: gxbb: set audio output clock hierarchy

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

Fixes: 738f66d3 ("clk: gxbb: add AmLogic GXBB clk controller driver")
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>