drm/rockchip: vop: Initialize vskiplines to zero

There is a path that use vskiplines with non-initialize.
That would cause vop abnormal behavior.
Signed-off-by: NMark Yao <mark.yao@rock-chips.com>

drivers/gpu/drm/rockchip/rockchip_drm_vop.c

@@ -310,7 +310,7 @@ static void scl_vop_cal_scl_fac(struct vop *vop, const struct vop_win_data *win,
 	uint16_t vsu_mode;
 	uint16_t lb_mode;
 	uint32_t val;
-	int vskiplines;
+	int vskiplines = 0;
 
 	if (dst_w > 3840) {
 		DRM_ERROR("Maximum destination width (3840) exceeded\n");