dm: pci: Make ranges dt property optional

dm: pci: Make ranges dt property optional

If we use U-Boot as coreboot payload with a generic dts without
any ranges specified we fail in pci pre_probe and our pci bus
is not usable.

So convert decode_regions(..) into a void function and do the simple
error handling there.

Signed-off-by: Christian Gmeiner <[email protected]>
Reviewed-by: Bin Meng <[email protected]>
[bmeng: fixed 'u-boot' in the commit message and checkpatch warning]
Signed-off-by: Bin Meng <[email protected]>
Reviewed-by: Simon Glass <[email protected]>