scsi: scsi_debug: replace SDEG_RES_IMMED_MASK with cmnd flag

This patch uses a cleaner method to convey the presence of the IMMED cdb
bit back to the generic delay code in the scsi_debug driver. The previous
method used a temporary mask over the SCSI result value (a 32 bit integer
soon to be restructured) that was not visible outside this driver. It has
still caused some confusion so a more conventional method is now used:
adding an extra flag to the scsi_cmnd "host_scribble" area.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>