clk: meson: axg-audio does not require syscon

The axg audio clock controller uses regmap mmio, not syscon.

Fixes: 1cd50181 ("clk: meson: axg: add the audio clock controller driver")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lkml.kernel.org/r/20190201125841.26785-4-jbrunet@baylibre.com