duplicate check for CAP_SYS_RAWIO

[Tong Zhang]

Kernel Version: 4.18.5

Problem Description:

We found a path where duplicate capability checks are observed,
the path is :

scsi_ioctl<- require CAP_SYS_ADMIN and CAP_SYS_RAWIO
     `->sg_scsi_ioctl() 
                `->blk_verify_command() <- require CAP_SYS_RAWIO

CAP_SYS_RAWIO is checked twice.

related file: 
  block/scsi_ioctl.c:215 
  block/scsi_ioctl.c:471
  drivers/scsi/scsi_ioctl.c:240
  drivers/scsi/scsi_ioctl.c:242

- Tong