block: Use child_of_bds in remaining places

Replace child_file by child_of_bds in all remaining places (excluding
tests).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200513110544.176672-28-mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/backup-top.c b/block/backup-top.c
index f059617..8af2c5f 100644
--- a/block/backup-top.c
+++ b/block/backup-top.c
@@ -215,8 +215,8 @@
              source->supported_zero_flags);
 
     bdrv_ref(target);
-    state->target = bdrv_attach_child(top, target, "target", &child_file, 0,
-                                      errp);
+    state->target = bdrv_attach_child(top, target, "target", &child_of_bds,
+                                      BDRV_CHILD_DATA, errp);
     if (!state->target) {
         bdrv_unref(target);
         bdrv_unref(top);