[SCSI] mvsas: performance improvement using domain_device->lldd_dev

Using sticky field to improve retrieve performance by eliminating some
lookups in . Remove some spurious casts.

Signed-off-by: Ying Chu <jasonchu@marvell.com>
Signed-off-by: Andy Yan <ayan@marvell.com>
Signed-off-by: Ke Wei <kewei@marvell.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>