The average long-term U.S. mortgage rate is holding at just above 6% after reversing a modest uptick in recent weeks just as the housing market closes in on the spring homebuying season. The benchmark 30-year fixed rate mortgage rate slipped to 6.09% from 6.11% last week, mortgage buyer Freddie Mac said Thursday. One year ago, the rate averaged 6.87%. The modest pullback brings the average rate back to where it was three weeks ago. Borrowing costs on 15-year fixed-rate mortgages, popular with