8250-men-mcb: fix signed/unsigned confusion

get_num_ports returns -ENODEV, and the result is stored in int, so it
should not be unsigned. Zero ports does not seem to make sense, so
make that check consistent.

Signed-off-by: Pavel Machek (CIP) <pavel@denx.de>

Link: https://lore.kernel.org/r/20200606151146.GA10940@amd


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>