dmsquash-live/apply-live-updates: Test proper file link.

Update flag link to /dev/root as required by commit
789668deb3.

modules.d/90dmsquash-live/apply-live-updates.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 
-if [ -L /run/rootfsbase ] && [ -d /run/initramfs/live/updates -o -d /updates ]; then
+if [ -h /dev/root ] && [ -d /run/initramfs/live/updates -o -d /updates ]; then
     info "Applying updates to live image..."
     mount -o bind /run $NEWROOT/run
     # avoid overwriting symlinks (e.g. /lib -> /usr/lib) with directories