meta-facebook: fix phosphor-gpio-monitor for usrmerge

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ib3f82c32379d2b92b0ceb23c294b02264f401d62
diff --git a/meta-facebook/recipes-phosphor/gpio/phosphor-gpio-monitor_%.bbappend b/meta-facebook/recipes-phosphor/gpio/phosphor-gpio-monitor_%.bbappend
index 398ccf7..c3e43ea 100644
--- a/meta-facebook/recipes-phosphor/gpio/phosphor-gpio-monitor_%.bbappend
+++ b/meta-facebook/recipes-phosphor/gpio/phosphor-gpio-monitor_%.bbappend
@@ -26,4 +26,4 @@
     install -d ${D}${libexecdir}/phosphor-gpio-monitor
     install -m 0777 ${WORKDIR}/ipmb-rescan-fru.sh ${D}${libexecdir}/phosphor-gpio-monitor/
 }
-FILES:${PN} += "/lib/systemd/system/obmc-ipmb-rescan-fru.service"
+FILES:${PN} += "${systemd_system_unitdir}/obmc-ipmb-rescan-fru.service"