dt-bindings: PCI: xilinx-cpm: Fix reg property order

All existing vendor DTSes are using "cpm_slcr" reg followed by "cfg" reg.

This order is also suggested by node name which is pcie@fca10000 which
suggests that cpm_slcr register should be the first.

Driver itself is using devm_platform_ioremap_resource_byname() for both
names that's why there is no functional change even on description which
are using current order.

But still prefer to change order to cover currently used description.
Fixes: e22fadb1 ("PCI: xilinx-cpm: Add YAML schemas for Versal CPM Root Port")

Signed-off-by: Bharat Kumar Gogada <bharat.kumar.gogada@xilinx.com>
Reviewed-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220516102217.25960-1-bharat.kumar.gogada@xilinx.com