gpu_group.c: check_scalar_live_ranges: take into account expansions
gpu_group.c: check_scalar_live_ranges: take into account expansions

The schedule trees from which kernels are extracted currently do not
contain any expansions, but this may change when statement instances
are combined during scheduling.
Take such expansions into account.

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

Meinersbur/ppcg,nicolasvasilache/ppcg,nicolasvasilache/ppcg,Meinersbur/ppcg