block: Convert bdrv_co_readv() to BdrvChild

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/crypto.c b/block/crypto.c
index ec1f247..87b1e00 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -428,7 +428,7 @@
         qemu_iovec_reset(&hd_qiov);
         qemu_iovec_add(&hd_qiov, cipher_data, cur_nr_sectors * 512);
 
-        ret = bdrv_co_readv(bs->file->bs,
+        ret = bdrv_co_readv(bs->file,
                             payload_offset + sector_num,
                             cur_nr_sectors, &hd_qiov);
         if (ret < 0) {