dm: core: Correct low cell in ofnode_read_pci_addr()

This reads the low cell of the PCI address from the wrong cell. Fix it.
Also fix the function that this code came from.

Fixes: 9e512045 (dm: core: Add operations on device tree references)
Fixes: 4ea5243a (fdt: fix fdtdec_get_pci_addr() for CONFIG_PHYS_64BIT)
Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>