can: ems_usb: ems_usb_start_xmit(): fix double dev_kfree_skb() in error path

There is no need to call dev_kfree_skb() when usb_submit_urb() fails
beacause can_put_echo_skb() deletes the original skb and
can_free_echo_skb() deletes the cloned skb.

Link: https://lore.kernel.org/all/20220228083639.38183-1-hbh25y@gmail.com
Fixes: 702171ad ("ems_usb: Added support for EMS CPC-USB/ARM7 CAN/USB interface")
Cc: stable@vger.kernel.org
Cc: Sebastian Haas <haas@ems-wuensche.com>
Signed-off-by: NHangyu Hua <hbh25y@gmail.com>
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/ems_usb.c

@@ -819,7 +819,6 @@ static netdev_tx_t ems_usb_start_xmit(struct sk_buff *skb, struct net_device *ne
 
 		usb_unanchor_urb(urb);
 		usb_free_coherent(dev->udev, size, buf, urb->transfer_dma);
-		dev_kfree_skb(skb);
 
 		atomic_dec(&dev->active_tx_urbs);