powerpc/pci: Remove unused struct pci_dn.pcidev field

In struct pci_dn, the pcidev field is assigned but not used, so remove it.

Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Acked-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>