CONTRIB: da: fix memory leak in dummy function da_atlas_open()

CONTRIB: da: fix memory leak in dummy function da_atlas_open()

The dummy function takes care of doing a bit of work using a malloc()
to avoid returning a constant but it doesn't free the tested pointer,
which coverity noticed in issue #741. Let's free it before testing it
for the return value.

This may be backported but is not important since this code is only
present to allow to build the device detection code and not to actually
run it.