Fix one more cast warning on Win32

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/12398009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13813 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ia32/macro-assembler-ia32.cc

@@ -648,7 +648,7 @@ Condition MacroAssembler::IsObjectNameType(Register heap_object,
                                            Register instance_type) {
   mov(map, FieldOperand(heap_object, HeapObject::kMapOffset));
   movzx_b(instance_type, FieldOperand(map, Map::kInstanceTypeOffset));
-  cmpb(instance_type, static_cast<int8_t>(LAST_NAME_TYPE));
+  cmpb(instance_type, static_cast<uint8_t>(LAST_NAME_TYPE));
   return below_equal;
 }