DALLAS — Cam Reddish might be out for a bit. The 22-year-old’s shoulder sprain was severe enough for him to leave the Knicks’ road trip for further tests in New York. Tom Thibodeau said he won’t have an update until the doctor’s evaluation, and the coach didn’t feel comfortable speculating until advised. Reddish sustained the injury Monday in Sacramento, where he fell hard onto the court after a soaring block attempt. Reddish jumped into the back of Kings guard Davion Mitchell and was upended from his legs. He tried to break the fall with his shoulder and sprained it, while also hitting his he…