clk: meson: axg-audio: fix regmap last register

Since the addition of the g12a, the last register is
AUDIO_CLK_SPDIFOUT_B_CTRL.

Fixes: 07500138 ("clk: meson: axg-audio: add g12a support")
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>