[SCSI] hpsa: allow SCSI mid layer to handle unit attention

We were clobbering the SCSI status and setting
cmd->result = DID_SOFT_ERROR << 16; to get a retry,
but better to let the mid layer handle the unit
attention.

Signed-off-by: Matt Gates <matthew.gates@hp.com>
Acked-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>