Stanse found an ommitted pci_dev_put on one error path in
cpcihp_generic_init. The path is taken on !dev, but also when
dev->hdr_type != PCI_HEADER_TYPE_BRIDGE. However it omits to
pci_dev_put on the latter.
As it is fine to pass NULL to pci_dev_put, put it in there
uncoditionally.