fix(emqx_retainer): fix dialyzer warnings

apps/emqx_retainer/src/emqx_retainer.erl

@@ -142,7 +142,8 @@ init([Env]) ->
     case mnesia:table_info(?TAB, storage_type) of
         Copies -> ok;
         _Other ->
-            {atomic, ok} = mnesia:change_table_copy_type(?TAB, node(), Copies)
+            {atomic, ok} = mnesia:change_table_copy_type(?TAB, node(), Copies),
+            ok
     end,
     StatsFun = emqx_stats:statsfun('retained.count', 'retained.max'),
     {ok, StatsTimer} = timer:send_interval(timer:seconds(1), stats),