drm/mediatek/mtk_disp_rdma: Fix formatting and supply missing struct member description

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

 drivers/gpu/drm/mediatek/mtk_disp_rdma.c:66: warning: Function parameter or member 'ddp_comp' not described in 'mtk_disp_rdma'
 drivers/gpu/drm/mediatek/mtk_disp_rdma.c:66: warning: Function parameter or member 'crtc' not described in 'mtk_disp_rdma'
 drivers/gpu/drm/mediatek/mtk_disp_rdma.c:66: warning: Function parameter or member 'data' not described in 'mtk_disp_rdma'

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-arm-kernel@lists.infradead.org
Cc: linux-mediatek@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/20201116174112.1833368-11-lee.jones@linaro.org

drivers/gpu/drm/mediatek/mtk_disp_rdma.c

@@ -56,8 +56,9 @@ struct mtk_disp_rdma_data {
 
 /**
  * struct mtk_disp_rdma - DISP_RDMA driver structure
- * @ddp_comp - structure containing type enum and hardware resources
- * @crtc - associated crtc to report irq events to
+ * @ddp_comp: structure containing type enum and hardware resources
+ * @crtc: associated crtc to report irq events to
+ * @data: local driver data
  */
 struct mtk_disp_rdma {
 	struct mtk_ddp_comp		ddp_comp;