Rename and fix ValueMap::resize to reserve

The underlying map type (DenseMap) has had its resize() function
renamed to reserve() as part of
c04fc7a60f (SVN 264026).

This is only visible when the member function is called, as it is
template type name dependent.

Differential Revision: https://reviews.llvm.org/D125387

llvm/include/llvm/IR/ValueMap.h

@@ -141,7 +141,7 @@ public:
   size_type size() const { return Map.size(); }
 
   /// Grow the map so that it has at least Size buckets. Does not shrink
-  void resize(size_t Size) { Map.resize(Size); }
+  void reserve(size_t Size) { Map.reserve(Size); }
 
   void clear() {
     Map.clear();