On PowerNV platform, we are holding an unnecessary refcount on a pci_dev, which
leads to the pci_dev is not destroyed when hotplugging a pci device.

This patch release the unnecessary refcount.
Signed-off-by: NWei Yang <weiyang@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>