meta-integrity: Convert to new override syntax

Signed-off-by: Armin Kuster <akuster808@gmail.com>

meta-integrity/recipes-core/systemd/systemd_%.bbappend

@@ -1,11 +1,11 @@
-FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
+FILESEXTRAPATHS:prepend := "${THISDIR}/files:"
 
 SRC_URI += " \
     file://machine-id-commit-sync.conf \
     file://random-seed-sync.conf \
 "
 
-do_install_append () {
+do_install:append () {
     for i in machine-id-commit random-seed; do
         install -d ${D}/${systemd_system_unitdir}/systemd-$i.service.d
         install -m 0644 ${WORKDIR}/$i-sync.conf ${D}/${systemd_system_unitdir}/systemd-$i.service.d