Fix overlapping registers in external array stores on x64.

R=danno@chromium.org
BUG=
TEST=

Review URL: http://codereview.chromium.org/6794047

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7498 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/lithium-x64.cc

@@ -1891,7 +1891,7 @@ LInstruction* LChunkBuilder::DoStoreKeyedSpecializedArrayElement(
       array_type == kExternalFloatArray;
   LOperand* val = val_is_temp_register
       ? UseTempRegister(instr->value())
-      : UseRegister(instr->key());
+      : UseRegister(instr->value());
   LOperand* key = UseRegister(instr->key());
 
   return new LStoreKeyedSpecializedArrayElement(external_pointer,