scsi: scsi_debug: Fix hrtimer support for ndelay

scsi: scsi_debug: Fix hrtimer support for ndelay

Since commit 771f712ba5b0 ("scsi: scsi_debug: Fix cmd duration
calculation"), ns_from_boot value is only evaluated in schedule_resp()
for polled requests.

However, ns_from_boot is also required for hrtimer support for when
ndelay is less than INCLUSIVE_TIMING_MAX_NS, so fix up the logic to
decide when to evaluate ns_from_boot.

Fixes: 771f712ba5b0 ("scsi: scsi_debug: Fix cmd duration calculation")
Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20241202130045.2335194-1-john.g.garry@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>