Quick compiler: fix compile-time perf regression

The recent changes to the temp register liveness tracking
introduced a measureable compile-time performance regression.
This CL cleans it up.

Change-Id: Id698b93e957f0ecab7ddfab94727f85e49cf10cf
diff --git a/compiler/dex/quick/mir_to_lir-inl.h b/compiler/dex/quick/mir_to_lir-inl.h
index b5b50a4..2973e14 100644
--- a/compiler/dex/quick/mir_to_lir-inl.h
+++ b/compiler/dex/quick/mir_to_lir-inl.h
@@ -25,7 +25,8 @@
 
 /* Mark a temp register as dead.  Does not affect allocation state. */
 inline void Mir2Lir::ClobberBody(RegisterInfo* p) {
-  if (p->IsTemp()) {
+  DCHECK(p->IsTemp());
+  if (!p->IsDead()) {
     DCHECK(!(p->IsLive() && p->IsDirty()))  << "Live & dirty temp in clobber";
     p->MarkDead();
     p->ResetDefBody();