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

Author: tttturtle-russ

Documentation/dev-tools/kmsan.rst

@@ -133,7 +133,7 @@ KMSAN shadow memory
 -------------------
 
 KMSAN associates a metadata byte (also called shadow byte) with every byte of
-kernel memory. A bit in the shadow byte is set iff the corresponding bit of the
+kernel memory. A bit in the shadow byte is set if the corresponding bit of the
 kernel memory byte is uninitialized. Marking the memory uninitialized (i.e.
 setting its shadow bytes to ``0xff``) is called poisoning, marking it
 initialized (setting the shadow bytes to ``0x00``) is called unpoisoning.