[SCSI] fix command retries in spi_transport class

The premise is that domain validation is likely to trigger errors which
it wants to know about, so the only time it should be retrying them is
when it gets a unit attention (likely as the result of a previous bus or
device reset).  Ironically, the previous coding retried three times in
all cases except those of unit attention.  The attached fixes this to do
the right thing.

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