inventory-manager: add Before stmt for service

Ensure the service advertises the primary object it
creates so that mapper-wait calls can be deferred by
systemd correctly.

Change-Id: I8510420320bc7f9d0327a5c0372eb14144392267
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/common/recipes-phosphor/inventory/phosphor-inventory-manager/xyz.openbmc_project.Inventory.Manager.service b/common/recipes-phosphor/inventory/phosphor-inventory-manager/xyz.openbmc_project.Inventory.Manager.service
index fe0d6d4..707e250 100644
--- a/common/recipes-phosphor/inventory/phosphor-inventory-manager/xyz.openbmc_project.Inventory.Manager.service
+++ b/common/recipes-phosphor/inventory/phosphor-inventory-manager/xyz.openbmc_project.Inventory.Manager.service
@@ -1,5 +1,6 @@
 [Unit]
 Description=Phosphor Inventory Manager
+Before=mapper-wait@-xyz-openbmc_project-inventory.service
 
 [Service]
 Restart=always