can: gs_usb: gs_can_open(): prevent memory leak

In gs_can_open() if usb_submit_urb() fails the allocated urb should be
released.

Fixes: d08e973a77d1 ("can: gs_usb: Added support for the GS_USB CAN devices")
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
