[SCSI] pm8001: fix endian issue with code optimization.

1. Fix endian issue.
2. Fix the following warning :
    " drivers/scsi/pm8001/pm8001_hwi.c:2932:32: warning: comparison
      between ‘enum sas_device_type’ and ‘enum sas_dev_type’".
3. Few code optimization.

Signed-off-by: Santosh Nayak <santoshprasadnayak@gmail.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>