Fix VirtualFrame::is_used for ARM

Caused a compiler warning when compiling on Windows.
Review URL: http://codereview.chromium.org/67108

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1705 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/virtual-frame-arm.h

@@ -85,7 +85,7 @@ class VirtualFrame : public Malloced {
   }
 
   bool is_used(Register reg) {
-    return is_used(reg.code()) != kIllegalIndex;
+    return is_used(reg.code());
   }
 
   // Add extra in-memory elements to the top of the frame to match an actual