Keep track of the link on the which the current request is in progress.
It allows support of links behind port multiplier.
Not all libata-sff is PMP compliant. Code for native BMDMA controller
does not take in accound PMP.
Tested on Marvell 7042 and Sil7526.
Signed-off-by: Gwendal Grignou <gwendal@google.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
ea3c64506e