Since ata_build_rw_tf() is only called from ata_scsi_rw_xlat() with the
tf, dev and tag arguments obtained from the queued command structure,
we can simplify the interface of ata_build_rw_tf() by passing directly
the qc structure as argument.

Furthermore, since ata_scsi_rw_xlat() is never used for internal
commands, we can also remove the internal tag check for the NCQ case.
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>