powerpc/pci: remove the multi-init for pci_dn->phb

pci_dn->phb is set to phb in update_dn_pci_info(), if succeed.

This patch removes the duplication of pci_dn->phb initialization.

Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>