ahci: Fix SDB FIS Construction

ahci: Fix SDB FIS Construction

The SDB FIS creation was mangled;
We were writing the error byte to byte 0,
and omitting the SDB FIS magic byte.

Though the SDB packet layout states that:
byte 0: Must be 0xA1 to indicate SDB FIS.
byte 1: Port multiplier select & other flags
byte 2: status byte.
byte 3: error byte.

This patch adds an SDB FIS structure with
human-readable names, and ensures that we
are filling the structure appropriately.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Michael S. Tsirkin <mst@redhat.com>
Message-id: 1412204151-18117-7-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>