scsi: ufs: cleanup struct utp_task_req_desc

Remove the pointless task_req_upiu and task_rsp_upiu indirections,
which are __le32 arrays always cast to given structures and just add
the members directly.  Also clean up variables names in use in the
callers a bit to make the code more readable.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>