[turbofan] Use load/store indexes as 64-bit registers on arm64.

src/compiler/arm64/code-generator-arm64.cc

Index: src/compiler/arm64/code-generator-arm64.cc
diff --git a/src/compiler/arm64/code-generator-arm64.cc b/src/compiler/arm64/code-generator-arm64.cc
index 58886ae19ebc06517467cd056c79a35e47a9b356..0c75b7c384327e39fc04d8831e3ea1b46e069231 100644
--- a/src/compiler/arm64/code-generator-arm64.cc
+++ b/src/compiler/arm64/code-generator-arm64.cc
@@ -100,8 +100,7 @@ class Arm64OperandConverter FINAL : public InstructionOperandConverter {
         return MemOperand(InputRegister(index + 0), InputInt32(index + 1));
       case kMode_MRR:
         *first_index += 2;
-        return MemOperand(InputRegister(index + 0), InputRegister(index + 1),
-                          SXTW);
+        return MemOperand(InputRegister(index + 0), InputRegister(index + 1));
     }
     UNREACHABLE();
     return MemOperand(no_reg);