It's not easy running a restaurant these days -- and it's not easy being an investor in most eatery stocks, either. Shares of Shake Shack (NYSE: SHAK), The Cheesecake Factory (NASDAQ: CAKE), and Habit Restaurants (NASDAQ: HABT) have suffered double-digit percentage declines this year, and at least one Wall Street pro thinks that things won't be getting better anytime soon.Nick Setyan at Wedbush downgraded the three restaurant stocks on Tuesday, going from outperform to neutral on all three investments.