scsi: scsi_debug: Drop scsi_debug_bus_reset() NULL pointer checks

scsi: scsi_debug: Drop scsi_debug_bus_reset() NULL pointer checks

The checks for SCSI cmnd, SCSI device, and SCSI host are unnecessary, so
drop them. Likewise, drop the NULL check for sdbg_host.

The only caller is scsi_try_bus_reset() -> eh_bus_reset_handler(), and
there those pointers cannot be NULL.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Link: https://lore.kernel.org/r/20230313093114.1498305-7-john.g.garry@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>