libata: Prevent interface errors with Seagate FreeAgent GoFlex

commit c531077f40abc9f2129c4c83a30b3f8d6ce1c0e7 upstream.

When using my Seagate FreeAgent GoFlex eSATAp external disk enclosure,
interface errors are always seen until 1.5Gbps is negotiated [1]. This
occurs using any disk in the enclosure, and when the disk is connected
directly with a generic passive eSATAp cable, we see stable 3Gbps
operation as expected.

Blacklist 3Gbps mode to avoid dataloss and the ~30s delay bus reset
and renegotiation incurs.

Signed-off-by: Daniel J Blueman <daniel@quora.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>