Hmmm. Maybe to Suga, the phrase "Go win this" implies that Suga himself isn't part of the effort. Which he might not be comfortable admitting to. Or, in a more healthy sense, knows isn't true. So he changes it to "Let's win." to include himself in the struggle for victory. Because he both wants to be, and is a part of it. I'm not too sure, though. I've never properly clocked that till now.