As a side effect, remove unused idetape_kfree_stage() and
idetape_abort_pipeline()

[bart: resurrect taking tape->lock + clearing IDETAPE_FLAG_PIPELINE_ACTIVE]
Signed-off-by: NBorislav Petkov <petkovbb@gmail.com>
Signed-off-by: NBartlomiej Zolnierkiewicz <bzolnier@gmail.com>