virtio_console: validate max_nr_ports before trying to use it

We calculate nr_ports based on the max_nr_ports:

nr_queues = use_multiport(portdev) ? (nr_ports + 1) * 2 : 2;

If the device advertises a large max_nr_ports, we will end up with a
integer overflow. Fixing this by validating the max_nr_ports and fail
the probe for invalid max_nr_ports in this case.

Cc: Amit Shah <amit@kernel.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20211019070152.8236-3-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>