drm/rockchip: vop: fix NV12 video display error

fixup the scale calculation formula on the case
src_height == (dst_height/2).
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
Reviewed-by: Sandy huang <sandy.huang@rock-chips.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1501494586-6984-1-git-send-email-mark.yao@rock-chips.com

drivers/gpu/drm/rockchip/rockchip_drm_vop.h

@@ -299,6 +299,9 @@ static inline uint16_t scl_get_bili_dn_vskip(int src_h, int dst_h,
 
 	act_height = (src_h + vskiplines - 1) / vskiplines;
 
+	if (act_height == dst_h)
+		return GET_SCL_FT_BILI_DN(src_h, dst_h) / vskiplines;
+
 	return GET_SCL_FT_BILI_DN(act_height, dst_h);
 }