They don’t lose an option year by bringing up Johnson. I believe he was already optioned to LV, which means that is good for the season. I’ll check.
From MLB.com: "An option year is used if a player spends 20 or more cumulative days in the minor leagues during a single season. Only one option is used per season, regardless of how many times the player is sent up or down.”
Johnson was optioned to LV on 4/21, so he can move up and down from the 40 to the 26 freely this season if that's right.