bindings: nvmem/zii: Fix location of nvmem.txt

The location pointed there is missing "bindings/" on its path.

Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Jonathan Corbet <corbet@lwn.net>