NVMEM documentation fix: A minor typo

This is a minor patch that fixes the following typo in the NVMEM documentation:

When a consumers no longer needs the NVMEM

to,

When a consumer no longer needs the NVMEM

Signed-off-by: Narendran Sankaran <naren.kernel@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>