powerpc/PCI: Add struct pci_ops member names to initialization

Some instances of pci_ops initialization rely on the read/write members'
location in the struct.  This is fragile and may break when adding new
members to the beginning of the struct.

No functional change.

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Arnd Bergmann <arnd@arndb.de>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <paulus@samba.org>
CC: Michael Ellerman <mpe@ellerman.id.au>
CC: linuxppc-dev@lists.ozlabs.org
CC: cbe-oss-dev@lists.ozlabs.org