can: kvaser_usb: free buf in error paths

commit 435019b4 upstream.

The allocated buffer was not freed if usb_submit_urb() failed.

Signed-off-by: Jimmy Assarsson <jimmyassarsson@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>