drm/mediatek: mtk_hdmi: Disgregate function mtk_hdmi_audio_set_param()

drm/mediatek: mtk_hdmi: Disgregate function mtk_hdmi_audio_set_param()

As a cleanup, and in preparation for splitting common bits of this
driver, disgregate the code in function mtk_hdmi_audio_set_param()
to the beginning and end of function mtk_hdmi_audio_hw_params().

In a later commit, the hw_params callback function will also be
disgregated so that the code will get two functions: one that
performs the generic hdmi_audio_param copy, and one that performs
IP specific setup, both of which will be called in the callback,
allowing all of the non IP version specific code to get moved in
a common file.

Reviewed-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20250415104321.51149-9-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>