Fix compile fail

src/emqx_sm_sup.erl

@@ -47,7 +47,7 @@ init([]) ->
               permanent, 5000, worker, [?HELPER]},
 
     %% SM Pool Sup
-    MFA = {emqttd_sm, start_link, []},
-    PoolSup = emqx_pool_sup:spec([emqttd_sm, hash, erlang:system_info(schedulers), MFA]),
+    MFA = {?SM, start_link, []},
+    PoolSup = emqttd_pool_sup:spec([?SM, hash, erlang:system_info(schedulers), MFA]),
     {ok, {{one_for_all, 10, 3600}, [Helper, PoolSup]}}.