Use the build system rules to compile the .proto files.

Change-Id: If5f98e50a40fdca88c69e889e952adc9f4170d77
diff --git a/mock-ril/src/cpp/experiments.cpp b/mock-ril/src/cpp/experiments.cpp
index 317fd9d..b6bda08 100644
--- a/mock-ril/src/cpp/experiments.cpp
+++ b/mock-ril/src/cpp/experiments.cpp
@@ -22,7 +22,7 @@
 #include "worker.h"
 #include "util.h"
 
-#include "ril.pb.h"
+#include "hardware/ril/mock-ril/src/proto/ril.pb.h"
 
 #include "logging.h"
 #include "js_support.h"