ide: use blk_fs_request() check in ide-taskfile.c

Use blk_fs_request() in ide-taskfile.c instead of checking for:
- rq->bio in ide_pio_datablock() and task_error()
- rq->cmd_type == REQ_TYPE_ATA_TASKFILE in task_end_request()

There should be no functional changes caused by this patch.

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