migration/colo: Tidy up bql_unlock() around bdrv_activate_all()

Make the code more tight.

Suggested-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Zhang Chen <chen.zhang@intel.com>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
[fixed mangled author email address]
Signed-off-by: Fabiano Rosas <farosas@suse.de>
diff --git a/migration/colo.c b/migration/colo.c
index ca37b93..f96c2ee 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -837,12 +837,11 @@
     /* Make sure all file formats throw away their mutable metadata */
     bql_lock();
     bdrv_activate_all(&local_err);
+    bql_unlock();
     if (local_err) {
-        bql_unlock();
         error_report_err(local_err);
         return NULL;
     }
-    bql_unlock();
 
     failover_init_state();