scx200_acb: Fix PCI device reference count

The scx200_acb driver supports two kind of devices, PCI ones and ISA
ones. Even ISA ones are detected using the presence of a given PCI
device, and we get a reference to it, but never put it back, so we
have a leak. Fix it.

Signed-off-by: Jean Delvare <khali@linux-fr.org>