isl_map_convex_hull: drop unused variable
isl_map_convex_hull: drop unused variable

Detected by a scan_build on Polly.

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

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