[SelectionDAG] Use SmallVectorImpl& to avoid repeating SmallVector size. NFC

Author: topperc

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -11872,7 +11872,7 @@ bool operator<(const UseMemo &L, const UseMemo &R) {
 /// pointed to by a UseMemo is deleted, set the User to nullptr to indicate that
 /// the node already has been taken care of recursively.
 class RAUOVWUpdateListener : public SelectionDAG::DAGUpdateListener {
-  SmallVector<UseMemo, 4> &Uses;
+  SmallVectorImpl<UseMemo> &Uses;
 
   void NodeDeleted(SDNode *N, SDNode *E) override {
     for (UseMemo &Memo : Uses)
@@ -11881,7 +11881,7 @@ class RAUOVWUpdateListener : public SelectionDAG::DAGUpdateListener {
   }
 
 public:
-  RAUOVWUpdateListener(SelectionDAG &d, SmallVector<UseMemo, 4> &uses)
+  RAUOVWUpdateListener(SelectionDAG &d, SmallVectorImpl<UseMemo> &uses)
       : SelectionDAG::DAGUpdateListener(d), Uses(uses) {}
 };