[ptr-compr][heap] Fix Heap::kPointerMultiplier

The multiplier should depend on the kTaggedSize.

Bug: v8:7703
Change-Id: I3a13e51d06c31b70f6191b23b1913e7bc35cdb8f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1708473
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62801}

src/heap/heap.h

@@ -233,8 +233,7 @@ class Heap {
   // should instead adapt it's heap size based on available physical memory.
   static const int kPointerMultiplier = 1;
 #else
-  // TODO(ishell): kSystePointerMultiplier?
-  static const int kPointerMultiplier = i::kSystemPointerSize / 4;
+  static const int kPointerMultiplier = i::kTaggedSize / 4;
 #endif
 
   static const size_t kMaxInitialOldGenerationSize =