docs/admin-guide/mm/ksm.rst fix intraface -> interface typo

Fix typo from 'intraface' to 'interface' in admin guide for KSM.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20230424080305.2985-1-donald.hunter@gmail.com


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