MIPS: Fix deoptimization failure in WordCompare

In case of deoptimization after WordCompare test, the control flow is lost in the
unoptimized version of the code because wrong register is used for comparision
(a0 instead of v0)

TEST=mjsunit/regress/regress-3717
BUG=

Review-Url: https://codereview.chromium.org/2160533003
Cr-Commit-Position: refs/heads/master@{#37845}

src/full-codegen/mips/full-codegen-mips.cc

@@ -736,7 +736,7 @@ void FullCodeGenerator::PrepareForBailoutBeforeSplit(Expression* expr,
   PrepareForBailout(expr, BailoutState::TOS_REGISTER);
   if (should_normalize) {
     __ LoadRoot(t0, Heap::kTrueValueRootIndex);
-    Split(eq, a0, Operand(t0), if_true, if_false, NULL);
+    Split(eq, v0, Operand(t0), if_true, if_false, NULL);
     __ bind(&skip);
   }
 }

src/full-codegen/mips64/full-codegen-mips64.cc

@@ -735,7 +735,7 @@ void FullCodeGenerator::PrepareForBailoutBeforeSplit(Expression* expr,
   PrepareForBailout(expr, BailoutState::TOS_REGISTER);
   if (should_normalize) {
     __ LoadRoot(a4, Heap::kTrueValueRootIndex);
-    Split(eq, a0, Operand(a4), if_true, if_false, NULL);
+    Split(eq, v0, Operand(a4), if_true, if_false, NULL);
     __ bind(&skip);
   }
 }