gpu.c: extract_single_tagged_access: clean up space copying
gpu.c: extract_single_tagged_access: clean up space copying

The copy of space is needed by isl_space_domain,
but it was being assigned to space2, which is subsequently overwritten.
In practice, this happens to work out because taking
a copy only changes the reference count and returns
the same pointer, but the original code is still confusing,
if not technically incorrect.

Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

Meinersbur/ppcg,Meinersbur/ppcg