drm/mediatek/mtk_disp_gamma: Strip and demote non-conformant kernel-doc header

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

drivers/gpu/drm/mediatek/mtk_disp_gamma.c:42: warning: Function parameter or member 'clk' not described in 'mtk_disp_gamma'
drivers/gpu/drm/mediatek/mtk_disp_gamma.c:42: warning: Function parameter or member 'regs' not described in 'mtk_disp_gamma'
drivers/gpu/drm/mediatek/mtk_disp_gamma.c:42: warning: Function parameter or member 'cmdq_reg' not described in 'mtk_disp_gamma'
drivers/gpu/drm/mediatek/mtk_disp_gamma.c:42: warning: Function parameter or member 'data' not described in 'mtk_disp_gamma'

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_gamma.c

···
 	bool has_dither;
 };
 
-/**
+/*
  * struct mtk_disp_gamma - DISP_GAMMA driver structure
- * @ddp_comp - structure containing type enum and hardware resources
- * @crtc - associated crtc to report irq events to
  */
 struct mtk_disp_gamma {
 	struct clk *clk;