elf2flt: change source site

The CVS repository for this package is no longer available. So
changing the repository to be a mirror git repository.

Fixes:
  http://autobuild.buildroot.net/results/779/77997fd75282c355f6270b92371c161c9457d1dd



Signed-off-by: Ryan Barnett <rjbarnet@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>