scsi: mvsas: Remove set but not used variable 'id'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/scsi/mvsas/mv_sas.c: In function 'mvs_work_queue':
drivers/scsi/mvsas/mv_sas.c:1909:31: warning:
 variable 'id' set but not used [-Wunused-but-set-variable]

It never used since introduction in commit
20b09c29

 ("[SCSI] mvsas: add support for 94xx; layout change; bug fixes")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>