drm/rockchip: vop2: Fix the port mux of VP2

The port mux of VP2 should be RK3568_OVL_PORT_SET__PORT2_MUX.

Fixes: 604be855 ("drm/rockchip: Add VOP2 driver")
Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240422101905.32703-2-andyshrk@163.com

drivers/gpu/drm/rockchip/rockchip_drm_vop2.c

@@ -2344,7 +2344,7 @@ static void vop2_setup_layer_mixer(struct vop2_video_port *vp)
 		port_sel |= FIELD_PREP(RK3568_OVL_PORT_SET__PORT2_MUX,
 			(vp2->nlayers + vp1->nlayers + vp0->nlayers - 1));
 	else
-		port_sel |= FIELD_PREP(RK3568_OVL_PORT_SET__PORT1_MUX, 8);
+		port_sel |= FIELD_PREP(RK3568_OVL_PORT_SET__PORT2_MUX, 8);
 
 	layer_sel = vop2_readl(vop2, RK3568_OVL_LAYER_SEL);