dm: device: fail uclass_find_first_device() if list_empty

While uclass_find_device() fails with -ENODEV in case of list_empty
strangely uclass_find_first_device() returns 0.

Fix uclass_find_first_device() to also fail with -ENODEV instead.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Simon Glass <sjg@chromium.org>