scsi: core: Rework scsi_host_block()

Make scsi_host_block() easier to read by converting it to the widely used
early-return style. See also commit f983622a ("scsi: core: Avoid
calling synchronize_rcu() for each device in scsi_host_block()").

Reviewed-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Cc: Ye Bin <yebin10@huawei.com>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230529202640.11883-2-bvanassche@acm.org


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>