drm/mediatek: mtk_drm_crtc: Use kmalloc in mtk_drm_crtc_duplicate_state

Optimize mtk_drm_crtc_duplicate_state() by switching from kzalloc() to
kmalloc(): the only variable of this struct that gets checked in other
functions is `pending_config`, but if that's set to false, then all of
the remaining variables will only ever be set, but not read - so, also
set `pending_config` to false.
This saves us some small overhead.

Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20220118133759.112458-2-angelogioacchino.delregno@collabora.com/


Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>