If JNIEnvExt is-a JNIEnv, we can lose a bunch of reinterpret_casts.

Likewise with JavaVM.

Change-Id: I505e42e9197951b6c82e6dbf8dcc1fc4dd5aad31
diff --git a/src/jni_compiler.cc b/src/jni_compiler.cc
index b03a016..c277157 100644
--- a/src/jni_compiler.cc
+++ b/src/jni_compiler.cc
@@ -25,7 +25,7 @@
   JniCallingConvention jni_conv(native_method);
   ManagedRuntimeCallingConvention mr_conv(native_method);
   const bool is_static = native_method->IsStatic();
-  static Offset functions(OFFSETOF_MEMBER(JNIEnvExt, fns));
+  static Offset functions(OFFSETOF_MEMBER(JNIEnvExt, functions));
   static Offset monitor_enter(OFFSETOF_MEMBER(JNINativeInterface, MonitorEnter));
   static Offset monitor_exit(OFFSETOF_MEMBER(JNINativeInterface, MonitorExit));