remove the use of instance_success as RPCS3#16849 did

Author: Kethen

rpcs3/Input/sdl_pad_handler.cpp

@@ -180,9 +180,7 @@ bool sdl_pad_handler::Init()
 	if (m_is_init)
 		return true;
 
-	const bool instance_success = sdl_instance::get_instance().initialize();
-
-	if (!instance_success)
+	if (!sdl_instance::get_instance().initialize())
 		return false;
 
 	if (g_cfg.io.load_sdl_mappings)