[InstCombine] Fix typo in comment (NFC)

As pointed out in post-commit review of D63060.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 42322e3..6812bedf 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1425,7 +1425,7 @@
   if (Instruction *SatAdd = foldToUnsignedSaturatedAdd(I))
     return SatAdd;
 
-  // usub.sat(A, B) + A => umax(A, B)
+  // usub.sat(A, B) + B => umax(A, B)
   if (match(&I, m_c_BinOp(
           m_OneUse(m_Intrinsic<Intrinsic::usub_sat>(m_Value(A), m_Value(B))),
           m_Deferred(B)))) {