Mark ReadBarrierJni as a direct entry point on MIPS32.

The ReadBarrierJni MIPS32 entry point is a direct reference
to the native (C++) method art::ReadBarrierJni.

Test: Build ART for MIPS32.
Bug: 12687968
Change-Id: I6475855f4696690a681f69931618a055be65a00a
diff --git a/runtime/arch/mips/entrypoints_init_mips.cc b/runtime/arch/mips/entrypoints_init_mips.cc
index 833ba1b..6697a8d 100644
--- a/runtime/arch/mips/entrypoints_init_mips.cc
+++ b/runtime/arch/mips/entrypoints_init_mips.cc
@@ -283,7 +283,7 @@
 
   // Read barrier.
   qpoints->pReadBarrierJni = ReadBarrierJni;
-  static_assert(!IsDirectEntrypoint(kQuickReadBarrierJni), "Non-direct C stub marked direct.");
+  static_assert(IsDirectEntrypoint(kQuickReadBarrierJni), "Direct C stub not marked direct.");
   qpoints->pReadBarrierMark = artReadBarrierMark;
   static_assert(IsDirectEntrypoint(kQuickReadBarrierMark), "Direct C stub not marked direct.");
   qpoints->pReadBarrierSlow = artReadBarrierSlow;