Wiktionary suggests that clivus is related to clino and clinatus. But it doesn't explain the connection. Is there some way that n in a verb becomes v in a related noun or adjective?
Wiktionary traces both words to the same PIE root, ḱley-.
clino is an example of what Weiss calls "nasal presents" (p. 406). In other words (very non-technically), the present form of some verbs has an infix -n-. vinco is another good example of this phenomenon.
v in clivus, on the other hand, is what happens to *u (in *uo) between vowels. There was a discussion about it here the other day (vacuus).