dt: temporarily disable subtree creation failure check

Usually we want to know when creating a subtree fails. However, while
introducing this patch set we have to modify the device tree and some
times have the code to create a subtree in both the binary tree and
the dynamically created tree.

So ignore failures about this for now and enable them once we got rid
of the binary device tree.

Signed-off-by: Alexander Graf <agraf@suse.de>
