migration: fix leak of src file on dst

The return path channel is possibly leaked. Fix it.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/migration/migration.c b/migration/migration.c
index c3218cd..b90e399 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -133,6 +133,11 @@
 {
     struct MigrationIncomingState *mis = migration_incoming_get_current();
 
+    if (mis->to_src_file) {
+        qemu_fclose(mis->to_src_file);
+        mis->to_src_file = NULL;
+    }
+
     qemu_event_destroy(&mis->main_thread_load_event);
 }