[SLP][NFC]Use MutableArrayRef instead of SmallVectorImpl& in param, NFC.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -10131,7 +10131,7 @@ ResTy BoUpSLP::processBuildVector(const TreeEntry *E, Args &...Params) {
   inversePermutation(E->ReorderIndices, ReorderMask);
   if (!ReorderMask.empty())
     reorderScalars(GatheredScalars, ReorderMask);
-  auto FindReusedSplat = [&](SmallVectorImpl<int> &Mask) {
+  auto FindReusedSplat = [&](MutableArrayRef<int> Mask) {
     if (!isSplat(E->Scalars) || none_of(E->Scalars, [](Value *V) {
           return isa<UndefValue>(V) && !isa<PoisonValue>(V);
         }))