* Add 'int dsc' argument to ->pc_callback method.

* Call ide_tape_handle_dsc() internally in ide_tape_callback()
  if dsc argument is set and update ide_pc_intr() accordingly.

There should be no functional changes caused by this patch.

Cc: Borislav Petkov <petkovbb@gmail.com>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>