[libata] libata-scsi.c: Add function parameter documentation

Add the documentation of parameters of ata_change_queue_depth to silence the warning of make xmldocs

Signed-off-by: Marcos paulo de Souza <marcos.mage@gmail.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>