frameworks/base: 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: modules using frameworks/base find headers
Bug: 63762847
Change-Id: I0f9f231acdebe460f279135462f43d3e32eff64d
diff --git a/media/jni/android_media_ImageReader.cpp b/media/jni/android_media_ImageReader.cpp
index c655b7c..fcc975c 100644
--- a/media/jni/android_media_ImageReader.cpp
+++ b/media/jni/android_media_ImageReader.cpp
@@ -31,7 +31,7 @@
 #include <android_runtime/android_view_Surface.h>
 
 #include <jni.h>
-#include <JNIHelp.h>
+#include <nativehelper/JNIHelp.h>
 
 #include <stdint.h>
 #include <inttypes.h>