isl_scheduler.c: compute_max_coefficient: round up half of minimal size
isl_scheduler.c: compute_max_coefficient: round up half of minimal size

Taking half is just a heuristic, but when the size is one,
the maximal coefficient should still be one rather than zero.
Rounding up is simpler than rounding down and then
adding a special case for one.

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

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