serial: 8250: Fix initialisation of Quatech cards with the AMCC PCI chip

Fix the initialisation of older Quatech serial cards which are fitted with
the AMCC PCI Matchmaker interface chip.

Signed-off-by: Jonathan Woithe <(jwoithe@just42.net)>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>