PCI: spear: Pass config resource through reg property

PCIe configuration space should be passed through reg property, rather than
through ranges property.  This patch does the correction for SPEAr13XX
SOCs.

Signed-off-by: Pratyush Anand <pratyush.anand@st.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Mohit Kumar <mohit.kumar@st.com>