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/native/android/asset_manager.cpp b/native/android/asset_manager.cpp
index 0e5e5c6..98e9a42 100644
--- a/native/android/asset_manager.cpp
+++ b/native/android/asset_manager.cpp
@@ -24,7 +24,7 @@
 #include <utils/threads.h>
 
 #include "jni.h"
-#include "JNIHelp.h"
+#include <nativehelper/JNIHelp.h>
 
 using namespace android;