can: kvaser_usb: Fix accessing freed memory in kvaser_usb_start_xmit()

The call to can_put_echo_skb() may result in the skb being freed. The skb
is later used in the call to dev->ops->dev_frame_to_cmd().

This is avoided by moving the call to can_put_echo_skb() after
dev->ops->dev_frame_to_cmd().

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jimmy Assarsson <jimmyassarsson@gmail.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>