can: gs_usb: gs_can_close(): add missing set of CAN state to CAN_STATE_STOPPED

After an initial link up the CAN device is in ERROR-ACTIVE mode. Due
to a missing CAN_STATE_STOPPED in gs_can_close() it doesn't change to
STOPPED after a link down:

| ip link set dev can0 up
| ip link set dev can0 down
| ip --details link show can0
| 13: can0: <NOARP,ECHO> mtu 16 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 10
|     link/can  promiscuity 0 allmulti 0 minmtu 0 maxmtu 0
|     can state ERROR-ACTIVE restart-ms 1000

Add missing assignment of CAN_STATE_STOPPED in gs_can_close().

Cc: stable@vger.kernel.org
Fixes: d08e973a ("can: gs_usb: Added support for the GS_USB CAN devices")
Link: https://lore.kernel.org/all/20230718-gs_usb-fix-can-state-v1-1-f19738ae2c23@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/gs_usb.c

@@ -1030,6 +1030,8 @@ static int gs_can_close(struct net_device *netdev)
 	usb_kill_anchored_urbs(&dev->tx_submitted);
 	atomic_set(&dev->active_tx_urbs, 0);
 
+	dev->can.state = CAN_STATE_STOPPED;
+
 	/* reset the device */
 	rc = gs_cmd_reset(dev);
 	if (rc < 0)