display-manager-autologin.sh: fix sddm detection

sddm doesn't ship with a /etc/sddm.conf as default so the old check
returned false.

dracut/vmklive/display-manager-autologin.sh

@@ -22,8 +22,7 @@ if [ -d ${NEWROOT}/etc/gdm ]; then
 fi
 
 # Configure sddm autologin for the kde iso.
-if [ -r ${NEWROOT}/etc/sddm.conf ]; then
-    mv ${NEWROOT}/etc/sddm.conf ${NEWROOT}/etc/sddm.conf.old
+if [ -x ${NEWROOT}/usr/bin/sddm ]; then
     cat > ${NEWROOT}/etc/sddm.conf <<_EOF
 [Autologin]
 User=anon