can: kvaser_usb: check number of channels returned by HW

It is needed to check the number of channels returned by the HW because it
cannot be greater than MAX_NET_DEVICES otherwise it will crash.

Signed-off-by: Olivier Sobrie <olivier@sobrie.be>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>