It’s a guitar riff for the ages. When you hear “dunh dunh dunhhh, duhn duhn duh-dunhhh…” you are immediately swept into the hard-rock song “Smoke On The Water” whether that’s your taste in music or not. You might even be moved to try your hand at some air-guitar moves of your own. The Deep Purple classic goes back more than 50 years, and lead singer Ian Gillan recently took some time out to reminisce about it and remark that in reality, at the time it wasn’t that big of a deal. “It was a filler track,” the 78-year-old told dpa about the song, recorded at a tumultuous session in Montreux, Swi…