pdc202xx_new: fix Promise TX4 support

In case of Promise TX4 the first PCI device is located at slot 1
and the second one is at slot 2 so the offset used by pci_get_slot()
should be "+1" and not "+2".

Thanks goes out to Markus Dietz for bugreport and testing this patch.

Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>