of: base: improve error msg in of_phandle_iterator_next()

Also print out the phandle ID on error message, as a debug aid.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Link: https://lore.kernel.org/r/20210114101127.16580-1-info@metux.net


Signed-off-by: Rob Herring <robh@kernel.org>