MIPS: port Ensure that GenerateStoreFastDoubleElement returns stored value on all paths.

Ported r8781 (ca7888b)

BUG=
TEST=

Review URL: http://codereview.chromium.org/7563002
Patch from Paul Lind <plind44@gmail.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8801 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/stub-cache-mips.cc

@@ -4459,11 +4459,18 @@ void KeyedStoreStubCompiler::GenerateStoreFastDoubleElement(
   } else {
     destination = FloatingPointHelper::kCoreRegisters;
   }
-  __ SmiUntag(value_reg, value_reg);
+
+  Register untagged_value = receiver_reg;
+  __ SmiUntag(untagged_value, value_reg);
   FloatingPointHelper::ConvertIntToDouble(
-      masm, value_reg, destination,
-      f0, mantissa_reg, exponent_reg,  // These are: double_dst, dst1, dst2.
-      scratch4, f2);  // These are: scratch2, single_scratch.
+      masm,
+      untagged_value,
+      destination,
+      f0,
+      mantissa_reg,
+      exponent_reg,
+      scratch4,
+      f2);
   if (destination == FloatingPointHelper::kFPURegisters) {
     CpuFeatures::Scope scope(FPU);
     __ sdc1(f0, MemOperand(scratch, 0));