KIRSKSTONE: overwrite syntax

Signed-off-by: Christophe Priouzeau <christophe.priouzeau@foss.st.com>

recipes-core/systemd/systemd-conf_%.bbappend

@@ -1,4 +1,4 @@
-do_install_append_stm32mpcommon() {
+do_install:append:stm32mpcommon() {
     # enable watchdog on systemd configuration
     if ${@bb.utils.contains('MACHINE_FEATURES','watchdog','true','false',d)}; then
         install -d ${D}${systemd_unitdir}/system.conf.d/