memory: correct the comment to DIRTY_MEMORY_MIGRATION

The dirty bit is DIRTY_MEMORY_MIGRATION. Correct the comment.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Message-Id: <20190426020927.25470-1-richardw.yang@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/memory.c b/memory.c
index bb2b71e..3071c4b 100644
--- a/memory.c
+++ b/memory.c
@@ -2584,7 +2584,7 @@
 
     MEMORY_LISTENER_CALL_GLOBAL(log_global_start, Forward);
 
-    /* Refresh DIRTY_LOG_MIGRATION bit.  */
+    /* Refresh DIRTY_MEMORY_MIGRATION bit.  */
     memory_region_transaction_begin();
     memory_region_update_pending = true;
     memory_region_transaction_commit();
@@ -2594,7 +2594,7 @@
 {
     global_dirty_log = false;
 
-    /* Refresh DIRTY_LOG_MIGRATION bit.  */
+    /* Refresh DIRTY_MEMORY_MIGRATION bit.  */
     memory_region_transaction_begin();
     memory_region_update_pending = true;
     memory_region_transaction_commit();