[OpenMP] Fix partial unrolling off-by-one.

Even though the comment description is ".unroll_inner.iv < NumIterations", the code emitted a BO_LE ('<=') operator for the inner loop that is to be unrolled. This lead to one additional copy of the body code in a partially unrolled. It only manifests when the unrolled loop is consumed by another loop-associated construct. Fix by using the BO_LT operator instead.

The condition for the outer loop and the corresponding code for tiling correctly used BO_LT already.

Fixes #55236