Real Madrid will have to take this game serious, because they need these 3 points more than we can say, because if Real Madrid didn’t win the two last games, then I don’t think they will be among the teams that will be present in the round of 16 this season, which means they have no hope anymore. Although they have the highest chance of winning the game against Salzburg, it is a home game for Real Madrid, so it will be like a sure win for Real Madrid with no stress. Moreover, as you mentioned, Real Madrid is better than them in terms of strength and many other aspects.
Real Madrid at this moment knows that every point counts in their quest to progress to the next round of the competition? A home game against Salsburg I think will be an easy one for Carlo Ancelotti's men to get all three points. The quality of players at Real Madrid can't be matched by that of Salsburg, and now that Real Madrid knows they might fail to progress to the knockout stages of the competition, you should expect nothing but their very best in that game. My prediction is that Real Madrid will win that game as well as register 2+ goals.
That would be nice to bet on if you are quite sure of that outcome. Because the probability of happening may be indeed high as they have the motivation to achieve such position. But don't bet high stakes as you can't still guarantee the results. Be conservative with the amount of your bet even if you feel you will hit it right.