sparc/PCI: replace pci_cfg_fake_ranges() with pci_read_bridge_bases()

The generic code to read P2P bridge windows is functionally equivalent
to the sparc-specific pci_cfg_fake_ranges(), so use the generic code.

The "if (!res->start) res->start = ..." removed from the I/O window code
here was an artifact of the Intel 1K window support from 9d265124 and
is no longer necessary (it probably was just cloned from x86 and was never
useful on sparc).

Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>