[ptr-compr] Correct size for tagged values in GetByteWidth

Bug: v8:8477
Change-Id: Id565bb8a4d420b715e3e89325786de699e30b22c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1517883Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60197}

src/compiler/backend/register-allocator.cc

@@ -75,8 +75,7 @@ int GetByteWidth(MachineRepresentation rep) {
     case MachineRepresentation::kTaggedSigned:
     case MachineRepresentation::kTaggedPointer:
     case MachineRepresentation::kTagged:
-      // TODO(ishell): kTaggedSize once half size locations are supported.
-      return kSystemPointerSize;
+      return kTaggedSize;
     case MachineRepresentation::kWord64:
     case MachineRepresentation::kFloat64:
       return kDoubleSize;