drm/mediatek/mtk_disp_color: Strip incorrect doc and demote header

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

drivers/gpu/drm/mediatek/mtk_disp_color.c:45: warning: Function parameter or member 'clk' not described in 'mtk_disp_color'
drivers/gpu/drm/mediatek/mtk_disp_color.c:45: warning: Function parameter or member 'regs' not described in 'mtk_disp_color'
drivers/gpu/drm/mediatek/mtk_disp_color.c:45: warning: Function parameter or member 'cmdq_reg' not described in 'mtk_disp_color'

Cc: Chun-Kuang Hu <[e-mail]>
Cc: Philipp Zabel <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Matthias Brugger <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/mediatek/mtk_disp_color.c

···
 	unsigned int color_offset;
 };
 
-/**
+/*
  * struct mtk_disp_color - DISP_COLOR driver structure
- * @ddp_comp: structure containing type enum and hardware resources
  * @crtc: associated crtc to report irq events to
  * @data: platform colour driver data
  */