It is a fact that Real Madrid couldn't score more than one goal in their last two La Liga games. But they were able to score more before these ones in the absence of Benzema as well (e.g. 4 goals vs Mallorca, 2 goals vs Betis).
Considering that I think the reason of this might be related to their thinking of the Champions League games as well. They need to keep things balanced in the end and maybe they don't want to push hard in the La Liga as long as they are able to win a game one way or another. But it is the truth that Benzema is a big factor that helps the number of goals the team score increase more in most of the games.
It is just a coincidence that Real Madrid could not score more than one goal since Benzema returned to the team, it does not have too much meaning, and i am sure the players and coach is not even looking or thinking about that.
A great club like Real Madrid cannot put one big tournament first before the other, they should have the quality and depth in their team to concentrate on the two tournaments and try to win it, and they do. Both the champions league and La Liga is very important to Real Madrid and every season they play the best way they can to try and win the both of them.