[SCSI] libsas: fixup NCQ for SATA disks

We actually had two problems: the one with the tag (which is fixed by
zeroing the tag before sending the taskfile to the sequencer) but the
other with the fact that we sent our first NCQ command to the device
before the sequencer had been informed of the NCQ tagging
capabilities.  I fixed the latter by moving the rphy_add() to the
correct point in the code after the NCQ capabilities are set up.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>