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

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>
Conflicts:
	drivers/misc/p2sb_emul.c
	drivers/misc/swap_case.c
	drivers/pci/pci_mpc85xx.c
	drivers/pci/pci_x86.c
	drivers/pci/pcie_mediatek.c
	drivers/pci/pcie_phytium.c
	drivers/power/acpi_pmc/pmc_emul.c

[backport of mainline commit c4e72c4ad8b7c2db9c868bd053c25344b95900b8]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-Id: Iee5347f9a131102f691ea79650b33bbb09c50926