PCI: cadence: Do not error if "cdns,max-outbound-regions" is not found

Now that "cdns,max-outbound-regions" is made an optional property, do
not error out if "cdns,max-outbound-regions" device tree property is
not found.

Link: http://lore.kernel.org/r/20201105165331.GA55814@bogus
Link: https://lore.kernel.org/r/20201106151107.3987-3-kishon@ti.com


Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>