memory: Don't dump disabled regions

This makes "info mtree" output readable again.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/memory.c b/memory.c
index 09e44b8..7419853 100644
--- a/memory.c
+++ b/memory.c
@@ -1601,7 +1601,7 @@
     const MemoryRegion *submr;
     unsigned int i;
 
-    if (!mr) {
+    if (!mr || !mr->enabled) {
         return;
     }