Fix double computation in TermRefWithSignature.newLikeThis

Used to compute `asMemberOf(prefix)` twice.

Author: DarkDimius

src/dotty/tools/dotc/core/Types.scala

@@ -1743,7 +1743,7 @@ object Types {
       if (symbol.exists && !candidate.symbol.exists) { // recompute from previous symbol
         val ownSym = symbol
         val newd = asMemberOf(prefix)
-        candidate.withDenot(asMemberOf(prefix).suchThat(_ eq ownSym))
+        candidate.withDenot(newd.suchThat(_ eq ownSym))
       }
       else candidate
     }