ide-tape: remove tape->cache_stage

Prior to allocating a new pipeline stage, the code checked for the existence of
a cached pipeline stage to use. Do away with and stick to normal pipeline
stages only.

[bart: keep idetape_kmalloc_stage() for now]

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>