external/scrypt: use proper nativehelper headers

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

Test: modules using external/scrypt find headers
Bug: 63762847
Change-Id: I9baf896015a1920f8a26daa2a0c549169628890f
diff --git a/crypto/scrypt/tests/scrypt_test.cpp b/crypto/scrypt/tests/scrypt_test.cpp
index ffb568d..7dfffe3 100644
--- a/crypto/scrypt/tests/scrypt_test.cpp
+++ b/crypto/scrypt/tests/scrypt_test.cpp
@@ -15,7 +15,7 @@
  */
 
 #define LOG_TAG "scrypt_test"
-#include <UniquePtr.h>
+#include <nativehelper/UniquePtr.h>
 #include <utils/Log.h>
 
 #include <gtest/gtest.h>