scsi: scsi_debug: Drop if with an always false condition

to_sdebug_host() is a container_of operation, so it never returns NULL.

Link: https://lore.kernel.org/r/20210506203206.254258-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>