Use the correct counter name for segment writer.

Else all Ra systems would use the same key and you would
only get segment writer counters for the last system to
start.

src/ra_log_segment_writer.erl

@@ -104,9 +104,10 @@ await(SegWriter)  ->
 %%%===================================================================
 
 init([#{data_dir := DataDir,
+        name := SegWriterName,
         system := System} = Conf]) ->
     process_flag(trap_exit, true),
-    CRef = ra_counters:new(?MODULE, ?COUNTER_FIELDS),
+    CRef = ra_counters:new(SegWriterName, ?COUNTER_FIELDS),
     SegmentConf = maps:get(segment_conf, Conf, #{}),
     {ok, #state{system = System,
                 data_dir = DataDir,