Enchanted creature gets +2/+2, has flying, and is a Demon in addition to its other types.
When Inner Demon enters the battlefield, all non-Demon creatures get -2/-2 until end of turn.
Inner Demon’s triggered ability affects only non-Demon creatures on the battlefield at the time it resolves. Creatures that enter the battlefield later in the turn won’t get -2/-2. Unless Inner Demon leaves the battlefield before that ability resolves, the enchanted creature won’t get -2/-2.