[PATCH] libata: err_mask misc fix

  1. ata_pio_complete():
     It seems unnecessary to wait for the clearing of the DRQ bit.
     (Waiting for BSY=0 should be enough.
     ata_ok() also checks the correctness of the status bits later.)

  2. ata_pio_block():
     - added error checking, before transfering data.
     - minor comments fix

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
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Signed-off-by: Jeff Garzik <jgarzik@pobox.com>