isl_convex_hull.c: collect_basic_maps: fix return type
isl_convex_hull.c: collect_basic_maps: fix return type

Internally, isl_basic_set_list and isl_basic_map_list are the same,
but it is still better to use the correct type.

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

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