The only occurrence on the web is in a Harry Potter/Buffy fanfic: Willow Tree Burning by Houses. In chapter 44:
Willow could smell mold and mildew, dark dank things, but also the delicious smell of magic, bright and hot, calling to her. She closed her eyes and let it flow in. It was right there for the taking, only one frail human body standing in the way. She could take down Voldemort; she could take down Giles and Rack and Warren. Surely little Peter Pettigrew would be no problem.
Not something you would have read in the 1980's. It's quite possible that many authors have used the same phrase.
If the phrase ever occurred in a Discworld novel, I guess that would be Sourcery (1988). But I while there are many passages about the attraction of magic, I don't remember reading about its smell.