Remove unused variable to please Clang.

src/ia32/stub-cache-ia32.cc

Index: src/ia32/stub-cache-ia32.cc
===================================================================
--- src/ia32/stub-cache-ia32.cc	(revision 5852)
+++ src/ia32/stub-cache-ia32.cc	(working copy)
@@ -1141,9 +1141,8 @@
   __ j(zero, miss, not_taken);
 
   // Check that the maps haven't changed.
-  Register reg =
-      CheckPrototypes(object, receiver, holder,
-                      scratch1, scratch2, scratch3, name, miss);
+  CheckPrototypes(object, receiver, holder,
+                  scratch1, scratch2, scratch3, name, miss);
 
   // Return the constant value.
   __ mov(eax, Handle<Object>(value));