By Rick Rothacker and Jochelle Mendonca (Reuters) - Wells Fargo & Co reported a higher-than-expected 23 percent rise in first-quarter profit on Friday, but its mortgage business showed further signs of slowing and net interest margins continued to shrink. Wells Fargo shares were down 2 percent at $36.78 in premarket trading. The fourth-largest U.S. bank by assets has emerged from the financial crisis as the leading U.S. home lender as other banks have pulled back from a business that burned them during the housing boom. ...