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/services/core/jni/onload.cpp b/services/core/jni/onload.cpp
index 5d7291a..05f140b 100644
--- a/services/core/jni/onload.cpp
+++ b/services/core/jni/onload.cpp
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include "JNIHelp.h"
+#include <nativehelper/JNIHelp.h>
 #include "jni.h"
 #include "utils/Log.h"
 #include "utils/misc.h"