sata_nv: allow changing queue depth

The sata_nv driver was missing the change_queue_depth hook in the SCSI host
template which the other NCQ-capable libata drivers had. This made it impossible
to change the queue depth by user request. Add this in.

Signed-off-by: Robert Hancock <hancockr@shaw.ca>
Signed-off-by: Jeff Garzik <jeff@garzik.org>