MIPS64: Use the Lsa() and Dlsa() macro/r6 instructions in existing code.

src/mips/code-stubs-mips.cc

Index: src/mips/code-stubs-mips.cc
diff --git a/src/mips/code-stubs-mips.cc b/src/mips/code-stubs-mips.cc
index 2dd61ba9463c42a81155a1d0fa3bd5f084cdb671..a19e82257f4cbe3eba80756ff8f9bcd57531db98 100644
--- a/src/mips/code-stubs-mips.cc
+++ b/src/mips/code-stubs-mips.cc
@@ -4054,10 +4054,8 @@ void NameDictionaryLookupStub::Generate(MacroAssembler* masm) {
     // Scale the index by multiplying by the entry size.
     STATIC_ASSERT(NameDictionary::kEntrySize == 3);
     // index *= 3.
-    __ mov(at, index);
     __ Lsa(index, index, index, 1);
 
-
     STATIC_ASSERT(kSmiTagSize == 1);
     __ Lsa(index, dictionary, index, 2);
     __ lw(entry_key, FieldMemOperand(index, kElementsStartOffset));