PCI: Remove __weak tag from pci_register_io_range()

pci_register_io_range() has only one definition, so there is no need for
the __weak attribute.  Remove it.

Tested-by: dann frazier <dann.frazier@canonical.com>
Signed-off-by: Gabriele Paoloni <gabriele.paoloni@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>