Camera: Rename CameraActionEvent duration

Rename "duration" field to correspond with the
actual time unit.

Bug: 139439353
Test: Successful build
Change-Id: I3e9b3ac5778d6fa4b6de35079743bdf6e85b7560
diff --git a/cmds/statsd/src/atoms.proto b/cmds/statsd/src/atoms.proto
index 2575542..882c28f 100644
--- a/cmds/statsd/src/atoms.proto
+++ b/cmds/statsd/src/atoms.proto
@@ -8189,7 +8189,7 @@
  */
 message CameraActionEvent {
     // Camera session duration
-    optional int64 duration = 1;
+    optional int64 duration_millis = 1;
 
     // Camera API level used
     optional int32 api_level = 2;