ide: remove now redundant ->cur_dev checks

* ->cur_dev should now be always valid if ->handler is set so
  remove redundant checks from ide_intr() and ide_timer_expiry().

* Apply CodingStyle fixups in ide_timer_expiry() while at it.

There should be no functional changes caused by this patch.

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