fixed a printf argument in the new logging stuff
diff --git a/aos/common/logging/logging_impl.cc b/aos/common/logging/logging_impl.cc
index 64696dc..147d6ba 100644
--- a/aos/common/logging/logging_impl.cc
+++ b/aos/common/logging/logging_impl.cc
@@ -113,7 +113,7 @@
 void PrintMessage(FILE *output, const LogMessage &message) {
   fprintf(output, "%s(%"PRId32")(%05"PRIu16"): %s at"
           " %010"PRId32".%09"PRId32"s: %s",
-          message.name, message.source, message.sequence,
+          message.name, static_cast<int32_t>(message.source), message.sequence,
           log_str(message.level), message.seconds, message.nseconds,
           message.message);
 }