[SCSI] SPI transport class, don't negotiate options not supported

At the moment, the transport class blindly tries to set things like
QAS and IU, even if the drive won't support them.  It's best not to
annoy the devices like this and instead only set what the drive says
is actually supported.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>