dm: sandbox: Add driver-model block-device support for sandbox

Update the host driver to support driver model for block devices. A future
commit will remove the old code, but for now it is useful to be able to use
it both with and without CONFIG_BLK.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Stephen Warren <swarren@nvidia.com>
diff --git a/include/sandboxblockdev.h b/include/sandboxblockdev.h
index 59f9519..5174f45 100644
--- a/include/sandboxblockdev.h
+++ b/include/sandboxblockdev.h
@@ -8,7 +8,9 @@
 #define __SANDBOX_BLOCK_DEV__
 
 struct host_block_dev {
+#ifndef CONFIG_BLK
 	struct blk_desc blk_dev;
+#endif
 	char *filename;
 	int fd;
 };