Fix race between sddm and logind

Make sure sddm is run after logind.
An explicit dependency will make sddm run after logind every time.

Closes: #978

services/sddm.service.in

@@ -2,7 +2,7 @@
 Description=Simple Desktop Display Manager
 Documentation=man:sddm(1) man:sddm.conf(5)
 Conflicts=getty@tty1.service
-After=systemd-user-sessions.service getty@tty1.service plymouth-quit.service
+After=systemd-user-sessions.service getty@tty1.service plymouth-quit.service systemd-logind.service
 
 [Service]
 ExecStart=@CMAKE_INSTALL_FULL_BINDIR@/sddm