PCI: Drop of_match_ptr() to avoid unused variables

We have stubs for most OF interfaces even when CONFIG_OF is not set, so we
allow building of most controller drivers in that case for compile testing.

When CONFIG_OF is not set, "of_match_ptr(<match_table>)" compiles to NULL,
which leaves <match_table> unused, resulting in errors like this:

  $ make W=1
  drivers/pci/controller/pci-xgene.c:636:34: error: ‘xgene_pcie_match_table’ defined but not used [-Werror=unused-const-variable=]

Drop of_match_ptr() to avoid the unused variable warning.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>