drm/mediatek/dp: fix memory leak on ->get_edid callback audio detection

The sads returned by drm_edid_to_sad() needs to be freed.

Fixes: e71a8ebb

 ("drm/mediatek: dp: Audio support for MT8195")
Cc: Guillaume Ranquet <granquet@baylibre.com>
Cc: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-mediatek@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: <stable@vger.kernel.org> # v6.1+
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20230914155317.2511876-1-jani.nikula@intel.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>