docs: staging: fix typo in docs

Resolve a spelling error in the documentation found
with codespell.

Signed-off-by: Vincenzo Mezzela <vincenzo.mezzela@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240208162748.111120-1-vincenzo.mezzela@gmail.com