Sometimes players just have a bad season. Martin was good for stretches last season, so odds are he's not "washed up." But the fact that he was playing in a role he was not accustomed to, perhaps had an undisclosed injury, or even a simple lack of confidence could have been the reason why.
My guess is that he corrects the problem, to a large degree, this season. He's a veteran and a pro who came out of perhaps the best defensive system in the history of hockey. Odds favor him being better this season, just saying.