firewire: sbp2: Fix SCSI sense data mangling

SCSI sense data in SBP-2/3 is carried in an unusual format that means we
have to un-mangle it on our end before we pass it to the SCSI subsystem.
Currently our un-mangling code doesn't quite follow the SBP-2 standard
in that we always assume Current and never Deferred error types, we
never set the VALID bit, and we mishandle the FILEMARK, EOM and ILI
bits.

This patch fixes the sense un-mangling to correctly handle those and
follow the spec.

Signed-off-by: Chris Boot <bootc@bootc.net>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>