However, given the following:
* He is a Hogwarts professor: Hogwarts is a school that emphasizes magic, with no indication of religious instruction.
* He is possessed by Voldemort: Voldemort, being a dark wizard, likely holds no interest in religion.
* His personality is meek and nervous: He doesn't seem to be the type of person who would hold strong religious convictions.
It's safe to assume that Professor Quirrell's religious beliefs, if any, are not a significant part of his character or plot.
J.K. Rowling has never made any official pronouncements about Professor Quirrell's religious beliefs, so any conclusion would be speculation.