can: kvaser_usb: Correct return value in printout

If the return value from kvaser_usb_send_simple_msg() was non-zero, the
return value from kvaser_usb_flush_queue() was printed in the kernel
warning.

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