unit: fix environment variable syntax

systemd populates an environment variable if it's in the format
'arg $value', but not for 'arg=$value'.

Change-Id: I89bd547909ee9203967630bb43e587dd4932da9e
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
diff --git a/meta-openbmc-machines/meta-openpower/common/recipes-phosphor/vpd/openpower-fru-vpd/op-vpd-parser.service b/meta-openbmc-machines/meta-openpower/common/recipes-phosphor/vpd/openpower-fru-vpd/op-vpd-parser.service
index 4c0add1..2e225a3 100644
--- a/meta-openbmc-machines/meta-openpower/common/recipes-phosphor/vpd/openpower-fru-vpd/op-vpd-parser.service
+++ b/meta-openbmc-machines/meta-openpower/common/recipes-phosphor/vpd/openpower-fru-vpd/op-vpd-parser.service
@@ -8,4 +8,4 @@
 Restart=no
 Type=oneshot
 EnvironmentFile={envfiledir}/obmc/inventory
-ExecStart={sbindir}/openpower-read-vpd --vpd=$EEPROM --fru=$FRUS --object=$PATHS
+ExecStart={sbindir}/openpower-read-vpd --vpd $EEPROM --fru $FRUS --object $PATHS