block: Fix how mirror_run() frees its buffer

It allocates with qemu_blockalign(), therefore it must free with
qemu_vfree(), not g_free().
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/mirror.c

@@ -225,7 +225,7 @@ static void coroutine_fn mirror_run(void *opaque)
     }
 
 immediate_exit:
-    g_free(s->buf);
+    qemu_vfree(s->buf);
     bdrv_set_dirty_tracking(bs, false);
     bdrv_iostatus_disable(s->target);
     if (s->should_complete && ret == 0) {