input: Docs: correct ntrig.rst typo

Fix a typo in ntrig.rst (found with 'codespell').

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: linux-input@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20220516002047.11395-1-rdunlap@infradead.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>