If "BSY=0, DRQ=0" condition happens on ATAPI just
complete the command as this condition happens for:
* the end of the PIO transfer (ie. REQUEST_SENSE
  seems to return only 18 of 96 requested bytes)
* unsupported ATAPI commands (ie. REPORT_LUNS)
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>