res_smdi: Fix shutdown ref.

When adding shutdown refs for OPTIONAL_API components I accidentally
added it to the unload_module function in res_smdi.  Move it to
load_module.

Change-Id: I2b9da38fbc11ef78ea23dbb2df92b684be7f647c

res/res_smdi.c

@@ -1377,6 +1377,9 @@ static int load_module(void)
 	ast_custom_function_register(&smdi_msg_retrieve_function);
 	ast_custom_function_register(&smdi_msg_function);
 
+	/* For Optional API. */
+	ast_module_shutdown_ref(AST_MODULE_SELF);
+
 	return AST_MODULE_LOAD_SUCCESS;
 }
 
@@ -1406,9 +1409,6 @@ static int _unload_module(int fromload)
 
 	smdi_loaded = 0;
 
-	/* For Optional API. */
-	ast_module_shutdown_ref(AST_MODULE_SELF);
-
 	return 0;
 }