serial: 8250_pci: Don't fail on multiport card class

serial: 8250_pci: Don't fail on multiport card class

BugLink: http://bugs.launchpad.net/bugs/1758886
commit e7f3e99cb1a667d04d60d02957fbed58b50d4e5a upstream.

Do not fail on multiport cards in serial_pci_is_class_communication().

It restores behaviour for SUNIX multiport cards, that enumerated by
class and have a custom board data.

Moreover it allows users to reenumerate port-by-port from user space.

Fixes: 7d8905d06405 ("serial: 8250_pci: Enable device after we check black list")
Reported-by: Nikola Ciprich <nikola.ciprich@linuxbox.cz>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Nikola Ciprich <nikola.ciprich@linuxbox.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>