Fix JNI compiler for mips64

Fix assembly instructions in JNI stub to store the right size. Fix
callee-saves in JNI calling convention to reflect return registers.
Fix pointer size in mips64 assembler.

Change-Id: I4eccd1f56f62fa9119918192ec424e9073398bc7
diff --git a/compiler/utils/mips64/assembler_mips64.cc b/compiler/utils/mips64/assembler_mips64.cc
index 233ae7d..388d274 100644
--- a/compiler/utils/mips64/assembler_mips64.cc
+++ b/compiler/utils/mips64/assembler_mips64.cc
@@ -1025,7 +1025,7 @@
   __ Move(A0, scratch_.AsGpuRegister());
   // Set up call to Thread::Current()->pDeliverException
   __ LoadFromOffset(kLoadDoubleword, T9, S1,
-                    QUICK_ENTRYPOINT_OFFSET(4, pDeliverException).Int32Value());
+                    QUICK_ENTRYPOINT_OFFSET(8, pDeliverException).Int32Value());
   __ Jr(T9);
   // Call never returns
   __ Break();