meta-phosphor: prep for new override syntax

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I588025b614416c43aa2d053765ab53bacf890cb5
diff --git a/meta-phosphor/recipes-phosphor/health/phosphor-health-monitor_git.bb b/meta-phosphor/recipes-phosphor/health/phosphor-health-monitor_git.bb
index 33ab360..4363d4c 100644
--- a/meta-phosphor/recipes-phosphor/health/phosphor-health-monitor_git.bb
+++ b/meta-phosphor/recipes-phosphor/health/phosphor-health-monitor_git.bb
@@ -18,4 +18,4 @@
 SRCREV = "2b231e8aa91a76a7c36f1c70c7e4058a38d0a5f1"
 S = "${WORKDIR}/git"
 
-SYSTEMD_SERVICE_${PN} = "phosphor-health-monitor.service"
+SYSTEMD_SERVICE:${PN} = "phosphor-health-monitor.service"