isl_ast_codegen.c: generate_next_level: use isl_ast_build_dim
isl_ast_codegen.c: generate_next_level: use isl_ast_build_dim

Do so instead of looking into the internals of the isl_ast_build.

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

tobig/isl,PollyLabs/isl,inducer/isl-mirror,tobig/isl,simbuerg/isl,SaberMod/isl-current,simbuerg/isl,evaautomation/isl,jleben/isl,Distrotech/isl,nicolasvasilache/isl,inducer/isl-mirror,nicolasvasilache/isl,SaberMod/isl-current,jleben/isl,UBERTC/isl,tobig/isl,SaberMod/isl-current,crossbuild/isl,inducer/isl-mirror,crossbuild/isl,simbuerg/isl,nicolasvasilache/isl,evaautomation/isl,BenzoSM/isl,Distrotech/isl,PollyLabs/isl,simbuerg/isl,simbuerg/isl,abduld/isl,PollyLabs/isl,BenzoSM/isl,evaautomation/isl,BenzoSM/isl,BenzoSM/isl,KangDroidSMProject/ISL,crossbuild/isl,abduld/isl,BenzoSM/isl,jleben/isl,evaautomation/isl,PollyLabs/isl,nicolasvasilache/isl,KangDroidSMProject/ISL,KangDroidSMProject/ISL,Distrotech/isl,nicolasvasilache/isl,Meinersbur/isl,KangDroidSMProject/ISL,UBERTC/isl,PollyLabs/isl,inducer/isl-mirror,abduld/isl,crossbuild/isl,Meinersbur/isl,UBERTC/isl,Meinersbur/isl,tobig/isl,jleben/isl,abduld/isl,Distrotech/isl,KangDroidSMProject/ISL,UBERTC/isl,inducer/isl-mirror,Distrotech/isl,jleben/isl,SaberMod/isl-current,Meinersbur/isl