btrfs: change the bg_reclaim_threshold valid region from 0 to 100

For the non-zoned case we may want to set the threshold for reclaim to
something below 50%.  Change the acceptable threshold from 50-100 to
0-100.
Tested-by: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/sysfs.c

@@ -744,7 +744,7 @@ static ssize_t btrfs_sinfo_bg_reclaim_threshold_store(struct kobject *kobj,
 	if (ret)
 		return ret;
 
-	if (thresh != 0 && (thresh <= 50 || thresh > 100))
+	if (thresh < 0 || thresh > 100)
 		return -EINVAL;
 
 	WRITE_ONCE(space_info->bg_reclaim_threshold, thresh);