[LoopVectorize][NFC] Fix incorrect comment in LoopVectorize.h

[benshi001]

// 1. The main loop pass that drives the different parts.
// 2. LoopVectorizationLegality - A unit that checks for the legality
//    of the vectorization.
// 3. InnerLoopVectorizer - A unit that performs the actual
//    widening of instructions.
// 4. LoopVectorizationCostModel - A unit that checks for the profitability
//    of vectorization. It decides on the optimal vector width, which
//    can be one, if vectorization is not profitable.

[fhahn]

LGTM, thanks for updating this!

llvm/include/llvm/Transforms/Vectorize/LoopVectorize.h

 // and generates target-independent LLVM-IR.
 // The vectorizer uses the TargetTransformInfo analysis to estimate the costs
 // of instructions in order to estimate the profitability of vectorization.
 //
 // The loop vectorizer combines consecutive loop iterations into a single
 // 'wide' iteration. After this transformation the index is incremented
 // by the SIMD vector width, and not by one.
 //
-// This pass has three parts:
+// This pass has four parts:
 // 1. The main loop pass that drives the different parts.
 // 2. LoopVectorizationLegality - A unit that checks for the legality
 //    of the vectorization.
 // 3. InnerLoopVectorizer - A unit that performs the actual
 //    widening of instructions.
 // 4. LoopVectorizationCostModel - A unit that checks for the profitability
 //    of vectorization. It decides on the optimal vector width, which
 //    can be one, if vectorization is not profitable.