I agree with what the others have posted so far, but with a couple of caveats. First, camera lenses may not produce a flat field, so your focus may be off in the periphery (if you focus for the center of the image). If you don't see this, or if you don't care, then just don't worry about it. The second caveat is that I've heard (hearsay alert!) that the heat from enlargers can cause problems for camera lenses, which by and large weren't designed for it. I wouldn't recommend you stop using a camera lens based on my very imperfect knowledge of this, but you might want to investigate this point further, particularly if your enlarger produces a lot of heat near the lens.
FWIW, I've got a couple of spare Russian Industar-96U 50mm enlarger lenses. If you want one I'd be willing to let it go cheap; just send me a PM.