tweak for readability (no functionality change)

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@124192 91177308-0d34-0410-b5e6-96231b3b80d8

include/tuple

@@ -589,7 +589,7 @@ typename tuple_element<_Ip, tuple<_Tp...> >::type&&
 get(tuple<_Tp...>&& __t)
 {
     typedef typename tuple_element<_Ip, tuple<_Tp...> >::type type;
-    return static_cast<typename tuple_element<_Ip, tuple<_Tp...> >::type&&>(
+    return static_cast<type&&>(
              static_cast<__tuple_leaf<_Ip, type>&&>(__t.base_).get());
 }