docs/dev-tools: fix a typo

docs/dev-tools: fix a typo

fix a typo in dev-tools/kmsan.rst

[jc: this is not really a typo, but "iff" is clearly a confusing construct
for non-native speakers; changing it will prevent people from trying to
"fix" it repeatedly.]

Signed-off-by: Haoyang Liu <tttturtleruss@hust.edu.cn>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20241015140159.8082-1-tttturtleruss@hust.edu.cn