ide-scsi: fix handling of DMA errors in idescsi_pc_intr()

Check return value of ->dma_end method and if there was a DMA error
handle it accordingly (set PC_FLAG_DMA_ERROR pc flag, don't update
pc->xferred and increase rq->errors).

Also move debug message in the right place while at it.

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