const-qualify Context::data

Makes it harder for people to accidentally write through it, which they
shouldn't be.

Change-Id: Icea11e9090e01813e3e7b4a15aad601d8b5478c7
diff --git a/aos/events/logging/logfile_utils.cc b/aos/events/logging/logfile_utils.cc
index 2cc2f61..123c579 100644
--- a/aos/events/logging/logfile_utils.cc
+++ b/aos/events/logging/logfile_utils.cc
@@ -113,8 +113,8 @@
     case LogType::kLogMessage:
     case LogType::kLogMessageAndDeliveryTime:
     case LogType::kLogRemoteMessage:
-      data_offset =
-          fbb->CreateVector(static_cast<uint8_t *>(context.data), context.size);
+      data_offset = fbb->CreateVector(
+          static_cast<const uint8_t *>(context.data), context.size);
       break;
 
     case LogType::kLogDeliveryTimeOnly: