SharedMemory cpp: use proper nativehelper headers

libnativehelper exports headers under nativehelper. These were
available before incorrectly as global headers in order to give
access to jni.h.

Test: cpp android.os.SharedMemory finds headers
Bug: 63762847
Change-Id: Ib1680c1f0508b457bbe17ca63375a53eeb071a25
diff --git a/core/jni/android_os_SharedMemory.cpp b/core/jni/android_os_SharedMemory.cpp
index 24d0811..1d29908 100644
--- a/core/jni/android_os_SharedMemory.cpp
+++ b/core/jni/android_os_SharedMemory.cpp
@@ -21,8 +21,8 @@
 #include <cutils/ashmem.h>
 #include <utils/Log.h>
 #include "JNIHelp.h"
-#include "JniConstants.h"
-#include "ScopedLocalRef.h"
+#include <nativehelper/JniConstants.h>
+#include <nativehelper/ScopedLocalRef.h>
 
 #include <algorithm>
 #include <errno.h>