init/functions: fix DispVM detection

init/functions

@@ -66,7 +66,7 @@ is_templatevm() {
 }
 
 is_dispvm() {
-    [ "$(qubes_vm_type)" = "DisposableVM" ]
+    [ "$(qubesdb-read /type)" = "DispVM" ]
 }
 
 is_fully_persistent() {