MIPS64: fix calling conventions in LoadClass and field accesses

This fixes failures in test 529-checker-unresolved

Change-Id: I6170c22059e9711b2fcc965b00d6e34edd839539
diff --git a/compiler/optimizing/code_generator_mips64.cc b/compiler/optimizing/code_generator_mips64.cc
index b36a042..9b78dec 100644
--- a/compiler/optimizing/code_generator_mips64.cc
+++ b/compiler/optimizing/code_generator_mips64.cc
@@ -2977,7 +2977,7 @@
   CodeGenerator::CreateLoadClassLocationSummary(
       cls,
       Location::RegisterLocation(calling_convention.GetRegisterAt(0)),
-      Location::RegisterLocation(A0));
+      calling_convention.GetReturnLocation(cls->GetType()));
 }
 
 void InstructionCodeGeneratorMIPS64::VisitLoadClass(HLoadClass* cls) {