PCI: hotplug/cpcihp, fix pci device refcounting

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.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Scott Murray <scott@spiteful.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>