schemas: Add SparePartNumber property

This commit adds property `SparePartNumber` under under interface
`xyz.openbmc_project.Inventory.Decorator.Asset` as described in [1].

[1] https://github.com/openbmc/phosphor-dbus-interfaces/blob/master/yaml/xyz/openbmc_project/Inventory/Decorator/Asset.interface.yaml

Change-Id: Id3c70edf0939404a25fd218190a044e1768a0ae0
Signed-off-by: Delphine CC Chiu <Delphine_CC_Chiu@wiwynn.com>
diff --git a/schemas/openbmc-dbus.json b/schemas/openbmc-dbus.json
index aa586a7..0b87b61 100644
--- a/schemas/openbmc-dbus.json
+++ b/schemas/openbmc-dbus.json
@@ -9,6 +9,9 @@
                         "Asset": {
                             "additionalProperties": false,
                             "properties": {
+                                "SparePartNumber": {
+                                    "type": "string"
+                                },
                                 "Manufacturer": {
                                     "type": "string"
                                 },