dm: pci: Update the PCI read_config() method to const dev *

At present this method uses a non-const udevice pointer, but the call
should not modify the device. Use a const pointer.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/pci/pcie_ecam_generic.c b/drivers/pci/pcie_ecam_generic.c
index 00644ed..c875f3a 100644
--- a/drivers/pci/pcie_ecam_generic.c
+++ b/drivers/pci/pcie_ecam_generic.c
@@ -35,8 +35,9 @@
  * code. Otherwise the address to access will be written to the pointer pointed
  * to by @paddress.
  */
-static int pci_generic_ecam_conf_address(struct udevice *bus, pci_dev_t bdf,
-					    uint offset, void **paddress)
+static int pci_generic_ecam_conf_address(const struct udevice *bus,
+					 pci_dev_t bdf, uint offset,
+					 void **paddress)
 {
 	struct generic_ecam_pcie *pcie = dev_get_priv(bus);
 	void *addr;
@@ -63,9 +64,9 @@
  * space of the device identified by the bus, device & function numbers in @bdf
  * on the PCI bus @bus.
  */
-static int pci_generic_ecam_read_config(struct udevice *bus, pci_dev_t bdf,
-				   uint offset, ulong *valuep,
-				   enum pci_size_t size)
+static int pci_generic_ecam_read_config(const struct udevice *bus,
+					pci_dev_t bdf, uint offset,
+					ulong *valuep, enum pci_size_t size)
 {
 	return pci_generic_mmap_read_config(bus, pci_generic_ecam_conf_address,
 					    bdf, offset, valuep, size);