[IR] Fix typo in trunc nuw semantics; NFC (#87285)

Author: programmerjake

llvm/docs/LangRef.rst

@@ -11448,7 +11448,7 @@ and converts the remaining bits to ``ty2``. Since the source size must
 be larger than the destination size, ``trunc`` cannot be a *no-op cast*.
 It will always truncate bits.
 
-If the ``nuw`` keyword is present, and any of the truncated bits are zero,
+If the ``nuw`` keyword is present, and any of the truncated bits are non-zero,
 the result is a :ref:`poison value <poisonvalues>`. If the ``nsw`` keyword
 is present, and any of the truncated bits are not the same as the top bit
 of the truncation result, the result is a :ref:`poison value <poisonvalues>`.