No, these spells are independent from your sorcerer class spells. A sorcerer gets their spell slots from their Spellcasting class feature. These spells are cast using the sorcerer's spell slots, which depend on the sorcerer's level.
The tiefling's spells from Devil's Tongue are not cast using the spell slots of any class.
The trait is a special ability that lets creatures cast spells without proper spell slots:
Some characters and Monsters have Special Abilities that let them cast spells without using spell slots. For example, a monk who follows the Way of the Four Elements, a Warlock who chooses certain eldritch invocations, and a Pit Fiend from the Nine Hells can all cast spells in such a way.
This ability is completely independent of spell slots gained from the tiefling's class levels.