isl_map_simplify.c: construct_test_ineq: use isl_basic_map_offset
isl_map_simplify.c: construct_test_ineq: use isl_basic_map_offset

This is a minor clean-up that reduces the dependence on the internal
representation.

Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

nicolasvasilache/isl,inducer/isl-mirror,Meinersbur/isl,nicolasvasilache/isl,nicolasvasilache/isl,PollyLabs/isl,tobig/isl,nicolasvasilache/isl,inducer/isl-mirror,tobig/isl,UBERTC/isl,tobig/isl,PollyLabs/isl,tobig/isl,Meinersbur/isl,UBERTC/isl,Meinersbur/isl,inducer/isl-mirror,PollyLabs/isl,nicolasvasilache/isl,inducer/isl-mirror,inducer/isl-mirror,PollyLabs/isl,Meinersbur/isl,UBERTC/isl,PollyLabs/isl,UBERTC/isl