By Dan Weil Data from the Mortgage Bankers Association show negative developments surrounding mortgages. The housing market continues to sour. An index of mortgage loan applications volume slumped a seasonally-adjusted 6.3% last week from a week earlier, according to the Mortgage Bankers Association. The MBA’s seasonally-adjusted index of mortgage applications for home purchases slid 3%. And the unadjusted index dropped 9% from a year ago. The index of mortgage applications for refinancings lost 10% from a week earlier and 62% from a year ago. “Mortgage application volume continues to decline …