drm/mediatek/mtk_disp_ovl: Strip and demote non-conformant header

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/mediatek/mtk_disp_ovl.c:83: warning: Function parameter or member 'clk' not described in 'mtk_disp_ovl'
 drivers/gpu/drm/mediatek/mtk_disp_ovl.c:83: warning: Function parameter or member 'regs' not described in 'mtk_disp_ovl'
 drivers/gpu/drm/mediatek/mtk_disp_ovl.c:83: warning: Function parameter or member 'cmdq_reg' not described in 'mtk_disp_ovl'
 drivers/gpu/drm/mediatek/mtk_disp_ovl.c:83: warning: Function parameter or member 'vblank_cb' not described in 'mtk_disp_ovl'
 drivers/gpu/drm/mediatek/mtk_disp_ovl.c:83: warning: Function parameter or member 'vblank_cb_data' not described in 'mtk_disp_ovl'

Cc: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-mediatek@lists.infradead.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602143300.2330146-4-lee.jones@linaro.org

drivers/gpu/drm/mediatek/mtk_disp_ovl.c

@@ -66,9 +66,8 @@ struct mtk_disp_ovl_data {
 	bool smi_id_en;
 };
 
-/**
+/*
  * struct mtk_disp_ovl - DISP_OVL driver structure
- * @ddp_comp: structure containing type enum and hardware resources
  * @crtc: associated crtc to report vblank events to
  * @data: platform data
  */