uboot-imx

dm: uclass: Add uclass_next_device_err() to return a valid device

Similarly to uclass_first_device_err(), add uclass_next_device_err()
which returns an error if there are no next devices in that uclass.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>