[vm] Fix regression in protobuf_encode benchmark.

Regression introduced in 1e24fe7.

Change-Id: I3a396058d2a2a30bef40b458c0f6bf1ba4fdbb54
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/106540
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google

runtime/vm/runtime_entry.cc

@@ -1392,7 +1392,7 @@ DEFINE_RUNTIME_ENTRY(SingleTargetMiss, 2) {
   // DBC does not use switchable calls.
   UNREACHABLE();
 #else
-  const Instance& receiver = Instance::CheckedHandle(zone, arguments.ArgAt(0));
+  const Instance& receiver = Instance::CheckedHandle(zone, arguments.ArgAt(1));
 
   DartFrameIterator iterator(thread,
                              StackFrameIterator::kNoCrossThreadIteration);