Fix missing seqlen_info param in softcap scoremod

[rucnyz]

Summary

apply_score_mod_inner in softmax.py calls score_mod with 7 arguments including seqlen_info introduced in #2043:

https://github.com/Dao-AILab/flash-attention/blob/main/flash_attn/cute/softmax.py#L457-L465

post_mod_scores = score_mod(
    score_ssa, batch_idx_ssa, head_idx_ssa,
    q_idx=q_idx_ssa, kv_idx=kv_idx_ssa,
    seqlen_info=seqlen_info,  # here
    aux_tensors=aux_args,
)

But create_softcap_scoremod in utils.py returns a function with only 6 parameters (missing seqlen_info):

https://github.com/Dao-AILab/flash-attention/blob/main/flash_attn/cute/utils.py#L120

def scoremod_premask_fn(acc_S_SSA, batch_idx, head_idx, q_idx, kv_idx, aux_tensors):

This causes TypeError: got an unexpected keyword argument 'seqlen_info' when using softcap.

Fix

Add seqlen_info parameter to scoremod_premask_fn signature to match apply_score_mod_inner.