psu-ng: Remove system from inventory mapper-wait

Update the service file for phosphor-psu-monitor to just wait for the
inventory service, not the /system inventory object specifically.
Waiting for the /system inventory object is unnecessary and can cause
delays in reaching BMC_READY state.

Signed-off-by: Brandon Wyman <bjwyman@gmail.com>
Change-Id: I5e1f1f271d0d3389b3a19a946e5360ad54de057c
diff --git a/services/phosphor-psu-monitor.service b/services/phosphor-psu-monitor.service
index 6c26565..df896c5 100644
--- a/services/phosphor-psu-monitor.service
+++ b/services/phosphor-psu-monitor.service
@@ -1,7 +1,7 @@
 [Unit]
 Description=Phosphor Power Supply Monitor
-Wants=mapper-wait@-xyz-openbmc_project-inventory-system.service
-After=mapper-wait@-xyz-openbmc_project-inventory-system.service
+Wants=mapper-wait@-xyz-openbmc_project-inventory.service
+After=mapper-wait@-xyz-openbmc_project-inventory.service
 Before=xyz.openbmc_project.State.Chassis.service
 
 [Service]