serial: use seperate getty template for serial ttys
diff --git a/units/getty@.service.m4 b/units/getty@.service.m4
index 01343c4..4b65d5b 100644
--- a/units/getty@.service.m4
+++ b/units/getty@.service.m4
@@ -30,7 +30,7 @@
 
 [Service]
 Environment=TERM=linux
-ExecStart=GETTY %I
+ExecStart=-GETTY %I
 Restart=restart-always
 RestartSec=0
 KillMode=process-group