[libata irq-pio] reorganize "buf + offset" in ata_pio_sector()

and __atapi_pio_bytes()

   - relocate DPRINTK("data %s\n", qc->tf.flags & ATA_TFLAG_WRITE ?
			"write" : "read");
   - buf + offset, buf - offset tidy up

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>