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

commit 9c5320f8d7d9a2cf623e65d50e1113f34d9b9eb1 upstream.

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>