Fix build warnings in ril.cpp.

Bug: 29401612
Change-Id: Icba225928f1336785cc5cb9a81e1c5b7b2121353
diff --git a/include/libril/ril_ex.h b/include/libril/ril_ex.h
index 8e15d65..692e4df 100644
--- a/include/libril/ril_ex.h
+++ b/include/libril/ril_ex.h
@@ -37,7 +37,7 @@
     RIL_SOCKET_ID socket_id;
     int fdListen;
     int fdCommand;
-    char* processName;
+    const char* processName;
     struct ril_event* commands_event;
     struct ril_event* listen_event;
     void (*processCommandsCallback)(int fd, short flags, void *param);