dt-bindings: 83xx-512x-pci: Drop cell-index property

28eac2b7 ("powerpc/fsl: Remove cell-index from PCI nodes"),
and for now it is still not used, drop it from doc.

Cc: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/pci/83xx-512x-pci.txt

@@ -9,7 +9,6 @@ Freescale 83xx and 512x SOCs include the same PCI bridge core.
 
 Example (MPC8313ERDB)
 	pci0: pci@e0008500 {
-		cell-index = <1>;
 		interrupt-map-mask = <0xf800 0x0 0x0 0x7>;
 		interrupt-map = <
 				/* IDSEL 0x0E -mini PCI */