external/neven: 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/neven find headers
Bug: 63762847
Change-Id: I73822e924e34eda84f087fb93532a0a10c8e7d0c
diff --git a/FaceDetector_jni.cpp b/FaceDetector_jni.cpp
index 6f59749..b31761c 100644
--- a/FaceDetector_jni.cpp
+++ b/FaceDetector_jni.cpp
@@ -27,7 +27,7 @@
 #include <android/bitmap.h>
 
 #include "jni.h"
-#include "JNIHelp.h"
+#include <nativehelper/JNIHelp.h>
 
 using namespace android;