MIPS: port Fix a typo in KeyedStoreIC, restore Kraken performance.

src/mips/stub-cache-mips.cc

Index: src/mips/stub-cache-mips.cc
diff --git a/src/mips/stub-cache-mips.cc b/src/mips/stub-cache-mips.cc
index 3e5a0091cab636108a9625f79745e2f157fb79c0..40c31fc0a1e3d004c1b74d51f71e05b31fa09ace 100644
--- a/src/mips/stub-cache-mips.cc
+++ b/src/mips/stub-cache-mips.cc
@@ -4201,7 +4201,7 @@ void KeyedStoreStubCompiler::GenerateStoreFastElement(MacroAssembler* masm,
   // have been verified by the caller to not be a smi.
 
   // Check that the key is a smi.
-  __ JumpIfNotSmi(a0, &miss_force_generic);
+  __ JumpIfNotSmi(key_reg, &miss_force_generic);
 
   // Get the elements array and make sure it is a fast element array, not 'cow'.
   __ lw(elements_reg,