Ensure hwmon doesn't start before object mapper available

Resolves openbmc/openbmc#2029

Change-Id: I978ddbeb773d22c77d4ee164b61c9f6fb15252bb
Signed-off-by: Andrew Geissler <andrewg@us.ibm.com>
diff --git a/common/recipes-phosphor/sensors/phosphor-hwmon/xyz.openbmc_project.Hwmon@.service b/common/recipes-phosphor/sensors/phosphor-hwmon/xyz.openbmc_project.Hwmon@.service
index a59349d..a091f1a 100644
--- a/common/recipes-phosphor/sensors/phosphor-hwmon/xyz.openbmc_project.Hwmon@.service
+++ b/common/recipes-phosphor/sensors/phosphor-hwmon/xyz.openbmc_project.Hwmon@.service
@@ -2,6 +2,7 @@
 Description=Phosphor Hwmon Poller
 ConditionFileNotEmpty=/etc/default/obmc/hwmon/%I.conf
 StopWhenUnneeded=true
+After=xyz.openbmc_project.ObjectMapper.service
 
 [Service]
 Restart=always