serial: 8250: moxa: Store num_ports in brd
When struct moxa8250_board is allocated, then num_ports should
be initialized in order to use it later in moxa8250_remove.
Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>