group_overlapping_writes: compute overlap with respect to innermost loop

group_overlapping_writes: compute overlap with respect to innermost loop

Before, we would also consider tile dimensions inside the innermost actual
loop, i.e., tile dimensions with a fixed value.  However, the copying
to and from shared memory takes places inside the innermost actual loop
and not inside those dimensions with a fixed value.
We should therefore consider access sets as overlapping even if they
occur for different values of those fixed dimensions.

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